CPSC 230 Computers and Programming I

CPSC 230Computers and Programming I

Fall 2004Dr. Lynn Lambert

This course will teach you: C++ Object-oriented concepts Programming Some stabs at problem solving

How computers work Computers understand machine

language only Each computer has its own

language All computer languages are in

binary (1s and 0s) No computer understands English,

Powerpoint, or C++

A computer program: Add X to Y and store in Z

In machine language: 01040100 (already simplified to decimal)

01050160 04040506 02060180

HUH!?

Assembly

Each machine instruction has matching, more English-like assembler:

Load X (was: 01040100) Load Y (was: 01050160) Add X Y Z (was: 04040506) Store Z (was: 02060180)Better, but … all this for one addition!?

C++

z=x+y;

Much better!

BUT, no machines understand source code. Only machine code.

Designing a Program1. Decide the problem to solve.

2. Design the solution!!!!!! 3. Translate design to C++4. Type the C++ program (source code) using

an editor (emacs): program.cc5. Compile (g++). Translates C++ into

machine language (object, machine, executable code)

6. Link (g++). Creates executable. Can be done with step 5 or separately.

7. Run the program (after 1-6).

At each step:

1. Think

2. Do

3. Debug

4. Test

Write a program to calculate the volume of a sphere Problem well-defined Design solution:

Read radius Calculate volume: V = 4/3r3

Print answer

Extreme Programming Also called Agile Programming,

Agile Methods Goal is to produce easily

modifiable, reliable code that corresponds to user wants

Pairs programming, tests created before program is written

Test for volume program Radius input: 2.0 // nice normal test

Answer should be: 33.5 Radius input: 2 // testing integer input

Answer should be: 33.5 Radius input: 0 // ALWAYS test for 0

Answer should be: 0 Others tests: negative, large, small,

etc.

C++ Program#include <iostream> // allows reading in and out

using namespace std; // standard namespace

int main() { float radius; // radius of a sphere float volume; // volume of sphere; float is decimal.// other types are int, char, bool, double

const float mypi = 3.14159; // const values cannot be changed // M_PI also defined in cmathcout << “This program calculates the

volume “ << “of a sphere given its radius.”

<< endl;// lots of other ways to do this cout. cout << “Enter the radius> “;cin >> radius;

// volume = 4/3 r3

try 1: volume = 4/3 M_PI r …? 3?try 2: volume = 4 / 3 * M_PI * r * r;try 2.b: volume = 4/3 * M_PI * pow(r, 3); // pow is in cmathcout << "The volume of a sphere with

radius ";cout << radius << " is " << volume <<

endl;return EXIT_SUCCESS; // in <cstdlib>}

Now, let’s do it

great. except it doesn't work.

int + int is int float + float is float

int - int is int float - float is float

int * int is int float * float is float

int / int is int float / float is float

Class Work

Write a program that converts a user entered number of inches to the equivalent number of centimeters (1 inch = 2.54 centimeters).

Work with your partner. Write an algorithm first Write the tests next (input value for what

variable, why this test, expected answer)

Gradually convert the algorithm to C++

FunctionsChapter 3

(modified from Deitel & Deitel web page)

Why functions? divide and conquer repeatable. reuse reliable code encapsulated

Program Components in C++

Modules: functions and classes Programs use new and “prepackaged”

modules New: programmer-defined functions, classes Prepackaged: from the standard library

Functions invoked by function call Function name and information

(arguments/parameters) it needs Function definitions

Only written once

Program Components in C++

Boss to worker analogy A boss (the calling function or caller)

asks a worker (the called function) to perform a task and return (i.e., report back) the results when the task is done

Library Functions Functions called by writing

functionName(argument1, argument2, …);

Perform common mathematical calculations Include the header file <cmath> Call the appropriate function

Library Functions Examplevolume = 4.0 / 3.0 * M_PI * pow(r, 3); pow (exponentiation) function returns

baseexponent (pow(2,3) would return 8) Other math functions listed on p. 173

of text All functions in math library return a double

Parameters/Arguments Function arguments can be

Constants sqrt( 4 );

Variables sqrt( x );

Expressions sqrt( sqrt( x ) ) ; sqrt( 3 - 6x );

Header Files Header files contain

Function prototypes Definitions of data types and

constants Header files ending with .h

Programmer-defined header files#include “myheader.h”

Library header files#include <cmath>

Other libraries Perform string operations, include

<string> Perform character manipulations,

include <cctype> file handling, <fstream> standard constants and routines

<cstdlib> Lots of others

To find a function or library Look in your textbook Ask your partner/class mates Ask me Look on google (or other search

engine) Look on google groups

Writing your own functions

To call a function, you need: Function call – invokes function execution done

To write your own function, you need: Function call (e.g., pow, sqrt). We know

this. Function prototype (shown in function libraries,

like <cmath> -- contains interface information) Function definition– contains the C++ that

defines how that function will be executed (e.g., main). Really, we know this.

Function call Calling/invoking a function

Tells C++ to go do function. If never called, never performed

nothing new. No change in how library functions, your functions are called

After finished, passes back result. Calling function can store or use result

x = pow(2, 3); cout << pow(2, 3);

Function Call Syntax

nameoffunction(arg1, arg2, …) square(x); Parentheses an operator used to call

function Pass argument x Function gets its own copy of arguments

Write a function call that prints the result of sqrt of 4. Discuss with 2 others.

Function definition Format for function definition

return-value-type function-name( parameter-list ){ declarations and statements}

Parameter list Comma separated list of arguments

Data type needed for each argument If no arguments, use void or leave blank

Return-value-type Data type of result returned (use void if nothing

returned)

Function definition Example function

int square( int y )

{

return y * y;

}

return keyword Returns data, and control goes to function’s caller

If no data to return, use return; Function ends when reaches right brace

Control goes to caller

Functions cannot be defined inside other functions

You try Write a function definition, sum3,

that returns the sum of 3 integers.

Function Prototypes Purpose

Tells compiler argument(s) type and return type of function

int square( int ); Function takes an int and returns an int

Syntax Function name Parameters (number and data type) Return type (void if returns nothing) Only needed if definition after function call semicolon (unlike header in function definition)

Function Prototypes Prototype must match function

header Function prototype

int sqr(int); Function Header in Function Definition

int sqr(int y){ …}

Write a function prototype for sum3

// Fig. 3.3: fig03_03.cpp. But modified from code in book// Creating and using a programmer-defined function.#include <iostream>#include <cstdlib> using namespace std; // modified from code in book int square( int ); // function prototype int main() { int number; // Ask user for number square then square that number cout << “This program calculates the square of an integer.”

<< endl; cout << “Enter a number> “; cin >> number; // next line is function call cout << number << “ squared is “ << square(number) << endl; return EXIT_SUCCESS; // indicates successful termination} // end main

Function call.: Parentheses () cause function to be called. When done, it returns the result.

Function prototype: specifies data types of arguments and return values. square expects and int, and returns an int.

function header: return typefunction name, parameter list.

function body: C++ statements in between {}s.

// this continues program begun on previous slide// square function definition returns // square of an integer int square( int y ) // y is a copy of argument to function{ return y * y; // returns square of y as an int } // end function square

OR

int square(int nbr){ int answer; answer = nbr * nbr; return answer;}

void Empty parameter lists

void or leave parameter list empty Indicates function takes no arguments Function print takes no arguments

and returns no value void print(); void print( void );

print function example Prototype

void printinfo(void); Function call

int main (){ ... printinfo(); …}

print function example cont'd function definition

void printinfo(){ cout << "this program calculates";

cout << " the area of a sphere"; cout << endl;}

void can be anywhere or nowhere

Return type OR argument list OR both or neither can be void

void printint(int x) int getint() void printinstructions() int square(int x)

Function overloading Function overloading

Functions with same name and different parameters

Should perform similar tasks i.e., function to square ints and function to

square floatsint square( int x) {return x * x;}

float square(float x) { return x * x; }

Similar to overloaded +, /, etc. operators

Function overloading cont'd Overloaded functions distinguished

by signature Based on position, number, and type of

parameters (order of parameters matters)

Name mangling Encodes function identifier with parameters

Type-safe linkage Ensures proper overloaded function called

// Fig. 3.25: fig03_25.cpp2 // Using overloaded functions.3 #include <iostream>4 5 using std::cout;6 using std::endl;7 8 // function square for int values 9 int square( int x ) 10 { 11 cout << "Called square with int argument: " << x << endl;12 return x * x; 13 14 } // end int version of function square 15 16 // function square for double values 17 double square( double y ) 18 { 19 cout << "Called square with double argument: " << y << endl;20 return y * y; 21 } // end double version of function square 23

24 int main()25 {26 int intResult = square( 7 ); // int version called27 double doubleResult;28 doubleResult = square( 7.5 ); // calls double version29 cout << "\nThe square of integer 7 is " << intResult30 << "\nThe square of double 7.5 is " 31 << doubleResult << endl; 32 33 return 0; // indicates successful termination34 35 } // end main

Called square with int argument: 7Called square with double argument: 7.5 The square of integer 7 is 49The square of double 7.5 is 56.25

Class Work With your partner, write a program

that calculates the volume of a sphere, and uses a function calcspherevolume.

Talk to your neighbors Use the book Use your notes

If Statements

Sections 1.25, 2.4-2.6

Control Structures All code thus far executes every

line of code sequentially We want to be able to repeat, to

choose some lines of code Three types of control: sequence,

conditional, repetition/iteration

Types of control structures Sequence – default in C++,

execute each instruction sequentially as it reached

Conditional – choose whether to execute some C++ statement (if, if -else switch)

Iteration – loop. Repeat some set of statements multiple times

Conditional Choose which statement to execute. Form: if (some condition is true), then do some action If (comparison) then (action) Many examples in English:

If raining, wear raincoat. If cold, wear winter coat.

When in Rome, do as the Romans (if in Rome, act like a Roman)

Conditionals in C++ If (comparison) then (action) Need a way to write the

comparison and the action Comparison is boolean expression

(evaluates to be true or false) Action is any (series of) C++

statements

ComparisonsBoolean expressions can have many

different forms: Using bool variables

bool shoulddoif=true; if (shoulddoif) // then do some action

Relational expression (compares values) Logical Expression (manipulates values

with and, or, not) Can be combined

Relational Operators

int x, y; x < y x <= y x > y x >= y x != y x == y // NOT x=y

Evaluating Boolean Expressions

true, false

0 is false Non-zero is true int x=3;

x is true. sometimes useful, but can cause problems

x=3 is NOT comparing x and 3.

Evaluating Boolean Expressions

int x=3; int y = 4; int z=5;

x < yx < y < zx = yy == 4z >= xx != 3(x + 4) < (y - 1)

truetrue, but tricky x is now 4, 4 is nonzero, so this

is true

truetruefalse7 < 3 false

Logical Operators and (&&, single & very different)

both values must be true for the expression to be true

if it is cold and rainy, wear your winter raincoat (if either isn't true, don't)

or (|| - on keyboard, called pipe symbol) either value can be true if it is cold or rainy, wear a coat (if one is true, do)

not (!) changes the truth value of the expression if it is not cold, do not wear a winter coat

Logical Operators

int x=3; int y=10;(x < y) && (y < 20)

(x == 3) || (y == 3)

x < y; 3 < 10; truey < 20; 10 < 20; truetrue && true is truex == 3 true.short circuit

evaluation(y==3 falsetrue || false is true)

More logical operators

int x=3; int y=10;!(y=10)

(x != 3) || (y != 3)

trick questiony=10 is 10 (true); !true is falsefalsex != 3 falsey != 3 truefalse || true is true

Yet more logical operators

int x=3; int y=10;!((x+1 < 4) ||(y <= 10))

!((x+1 < 4) &&(y <= 10))

x+1 = 44 < 4 false.keep

goingy <= 10 truefalse || true true! true is false4 < 4 false. DONE

with &&. Do not look at y <=10.

!false true

if statements if statement form:

if (boolean expression) c++ statement

if (x < y) cout << "x < y" << endl;

if statements cautions MUST have ()s around boolean

expression no syntax error for non-boolean like

expressions only ONE statement in an if

statement no ';' after if condition Make sure you account for values

that are equal

Your turn Write an if statement to assign x to

y if x is greater than y Discuss with 2 others

if-else If you want to do one thing if a condition is

true and something else if not, use if-else. form: if (condition)

C++ statement else C++ statement

if (x < y) cout << x << " is less than the other number"; else cout << y << " is less than the other number";

> one statement in an ifIf you want to have more than one statement

inside an if or an else, use {}s:if (x < y) { cout << x << " is less than the other number";

x = 0; } else { cout << y << " is less than the other number";

y = 0; }

If-else cautions either if clause or else clause or

both may have {}s. After statements inside if and else

clause are executed, control passes back to next sequential statement

no ';' after else Make sure you account for values

that are equal

Watch Out

if (3 < 4) x = 3;else cout << "3 < 4 is false" << endl; x = 0;cout << "the value of x is " << x <<

endl;

Embedded ifs If statements and if-else

statements may be embedded (if within if). simply evaluate them as the C++ code is executed:

if-else example is most common. sets up a table of conditions

Embedded if-else

F<60

D60-69

C70-79

B80-89

A>90

GradeAverage

Embedded if-else for tableif (ave >= 90) grade = 'A';else if ((ave < 90) && (ave >= 80)) // note: need ()s around entire condition grade = 'B'; else if ((ave < 80) && (ave >=70)) grade = 'C';else if ((ave < 70) && (ave >=60)) grade = 'D';else if ((ave < 70) && (ave < 60)) grade = 'F';

Tracing through the embeded if

Fixing the embedded ifif (ave >= 90) grade = 'A';else if (ave >= 80)// We know (ave < 90) or we wouldn't be

here grade = 'B'; else if (ave >=70) // we know ave < 80 grade = 'C';else if (ave >=60) grade = 'D';else // if ((ave < 70) && (ave < 60)) grade = 'F';

Cautions for embedded ifs Don't use redundant comparisons Make sure you check for values

that are equal Account for out of range values

Program style Put {}s on a line by themselves indent {}s 2-3 spaces, statements

one more than that All code outside if statements

should line up All code inside of if statements

should line up.

More complicated embedded ifsif (x < 3) if (y < 6) cout << "x and y between 3 and 6"; else cout << "x < 3; y >= 6";else if (y > 6) cout << "x and y not in 3-6 range"; else cout << "x >= 3; y <= 6";

You do it Writing if statements (on the same

paper you used earlier)

Loops

2.7-2.20

Repetition/Iteration Do some (series of) actions as long

as some condition exists “drive until you see a stop sign”

action repeated: drive condition: seeing a stop sign

Two parts of a loop: when to stop, what to repeat

Parts of a loop Condition: tells loop when to stop.

Critical that loop stops. Repeated actions: reason for doing

loop Update condition inside loop (get

closer to loop stopping eventually) Initialization: what is necessary to

do before loop is entered

Writing Loops

Answer the questions: What is the condition that will end the

loop? What actions should be repeated How can I update the condition inside

the loop so that it will stop eventually? What variables do I need to initialize

before the loop begins?

Ending Loops when program is running

ctrl-c end input/outputctrl-d end of filectrl-z stop job

Loops in C++ while do-while for

All loops can be written using only the while statement.

while statementwhile (condition)

action;usually:while (condition) { action; }Semantics: as long as condition is true, go

into loop, do series of actions, then go back up and check condition

C++ while

while (condition){ … C++ statements; ….

}

condition is boolean expression we know about

C++ statements we know about

while cautions could execute loop 0 times make sure loop stops all the same cautions as ifs

must have ()s no ; after () watch for expressions inside condition

that are not intended to be boolean expressions (especially = vs ==)

Sample while Sum the numbers 1-3 Do it the same way you would,

with an accumulator

count = 1;sum = 0;while (count <= 3) {sum = sum + count; count = count + 1; }cout << "The sum of integers from 1 to 3

is " << sum << endl;

Sum numbers 1-3

1 ??

count sum



Sum numbers 1-3

1 0

count sum

count = 1;sum = 0;while (count <= 3) {sum = sum + count; count = count + 1; }cout << "The sum of integers from 1 to 3 is

" << sum << endl;

// count <= 3 is true, so go into loop

Sum numbers 1-3

1 0

count sum



Sum numbers 1-3

1 0+1=1

count sum



Sum numbers 1-3

1+1=2 1

count sum


" << sum << endl;


Sum numbers 1-3

2 1

count sum



Sum numbers 1-3

2 1+2=3

count sum



Sum numbers 1-3

2+1=3 3

count sum


" << sum << endl;


Sum numbers 1-3

3 3

count sum

count = 1;sum = 0;while (count <= 3) {sum = sum + count; count = count + 1; } cout << "The sum of integers from 1 to

3 is " << sum << endl;

Sum numbers 1-3

3 3+3=6

count sum

count = 1;sum = 0; while (count <= 3) {sum = sum + count; count = count + 1; }cout << "The sum of integers from 1 to 3


Sum numbers 1-3

3+1=4 6

count sum


" << sum << endl;

// count <= 3 is false, so skip loop

Sum numbers 1-3

4 6

count sum


" << sum << endl;

The sum of integers from 1 to 3 is 6.

Sum numbers 1-3

4 6

count sum

Modify loop so it goes n timescount = 1;cout << "Enter an integer I should sum to> :";cin >> n;sum = 0;while (count <= n) {sum = sum + count; count = count + 1; }cout << "The sum of integers from 1 to " << n

<< " is " << sum << endl;

many common kinds of loops Count controlled – know how many time

you go through loop before you enter (not before you run the program)

validation – keep going until user enters a valid value

sentinel – keep going until a stopping value is reached

event-controlled – general. keep going until some event occurs.

Template for Count ControlledMemorize the templates

Init counter to 0 while (count < n) // n is number of times through loop { // all actions in loop count = count + 1; }

Count-controlled loop hints often implemented as a for

statement init counter before entering loop increment counter as the last

statement in the loop comparison is <= if count starts at

1 and < if count starts at 0.

Write a loop to get answer to A/B/C question

answer = 'P';while ((answer != 'A') && (answer != 'B') &&

(answer != 'C')) { cout << "Enter your answer (must be " << "A, B, or C> "; cin >> answer; answer = toupper(answer); //in <cctype> }

Another ABC versioncout << "Enter your answer ";cout << "(please enter A, B, or C)> ";cin >> answer; // if A, B, or C, loop is skippedanswer = toupper(answer); // help user somewhile ((answer != 'A') && (answer != 'B') &&

(answer != 'C')) { cout << " Your answer must be an A, " << "B, or C. Please enter again> "; cin >> answer; answer = toupper(answer); // in <cctype> }

Validation loop templatecout << "Enter a value> ";cin >> value;// vv1 .. vvn are all of the valid valueswhile ((value != vv1) && … (value != vvn)) {cout << "Your entry is invalid."; cout << "Enter a " << vv1 << ", " << … << "vvn> "; cin >> value; }

Validation loop hints prompt and cin immediately before

loop (or initialize to invalid value)

condition is (value != okvalue) && (value != otherokvalue) … put prompt and cin immediately

before condition is checked (at bottom of loop)

hints for writing loops Determine what kind of loop Write the template for that kind of

loop Determine the condition Determine what inside the loop will

update the condition Determine other things to do in loop Does condition need to be initialized?

Your turn On a piece of paper that you can

give me, write a loop to ensure that the user has entered a single digit (read the value in as a character). You may do range checking (>= 0 and < 10) or check each value

Discuss with 2 others

Write a loop to find the maximum of a list of numbers First, find max of 10 numbers

count controlled loop, so use count controlled template:Init counter to 0 while (count < n) // n is number of times through loop { // all actions in loop count = count + 1; }

Filling in Max finding loop

count = 0; // Init counter to 0 while (count < 10) // 10 is number of times through loop { // read a number and save max count = count + 1; }cout << "The maximum of the numbers you " << "entered is " << max << endl;

Filling in Max-Finding loopcount = 0; // Init counter to 0 while (count < 10) { cout << "Enter a number> "; cin >> number; // save max count = count + 1; }cout << "The maximum of the numbers you " << " entered is " << max << endl;

Finding max

same way as you finding max – start with one number being max, then compare each new number to max:

if (number > max) // max holds max so far

max = number;

// else otherwise, DO NOTHING!!!

Write a count controlled loop to find max of 10 numberscount = 0; // Init counter to 0 while (count < 10) { cout << "Enter a number> "; cin >> number; if (number > max) // max holds max so far

max = number;

count = count + 1; }cout << "The maximum of the numbers you" << " entered is " << max << endl;


max = number;

count = count + 1; }cout << "The maximum of the numbers you entered " << " is " << max << endl;

0 ??

count max

??

number


max = number;


0 ??

count max

0 < 10 true

??

number


max = number;


0 ??

count max

Enter a number>

??

number


max = number;


0 ??

count max

Enter a number> 23

23

number


max = number;


0 ??

count max

number > max ??? we don’t know. max is not initialized

23

number

Finding max in a loop Lessons

always initialize variables if necessary (number not initialized, but ok)

Always trace through/step through program to look for problems

Fixes Initialize max to be very low number so it

will be replaced immediately Read in a number before going into the loop

Write a count controlled loop to find max of 10 numbers

int count = 0; // can initialize when declareddouble number, max;cout << "Enter a number> ";cin >> max; // put number right into maxcount = 1; // Init counter to 1 because 1 number readwhile (count < 10) // don't do <= { cout << "Enter a number> "; cin >> number; if (number > max) // max holds max so far

max = number;


Your turn Write a count controlled loop to

find the minimum of n numbers (ask the user to enter n first)

Sentinel Controlled Loops Keep going until some value is entered. Template:cout << "Enter a value> ";cin >> value;while (value != sentinel) { // do loop processing cout << "enter a value> "; cin >> value; }

Write a loop to sum values until –1 is entered templatecout << "Enter a value> ";cin >> value;while (value != sentinel) { // do loop processing cout << "enter a

value> "; cin >> value; }

sum = 0;cout << "Enter a value> ";cin >> value;while (value != -1) { sum = sum + value; cout << "enter a value> "; cin >> value; }

More Your Turn Write a loop to find the max number

until a 0 is entered Write a loop to find the max of 6

numbers Write a loop that finds the smallest

of 8 numbers Write a loop that validates user

input until user enters a letter (use isalpha)

Write a loop to find the max number until a 0 is enteredcout << "Enter a value>

";cin >> value;while (value != sentinel) { // do loop processing cout << "enter a value>

";

cin >> value; }

cout << "Enter a value> ";cin >> value;max = value;while (value !=0) { if (value > max) max = value; cout << "enter a value> ";

cin >> value; }

Write a loop to find the max of 6 numbers

count = 0;max = -99999999;while (count < 6){cout << "Enter a number>

"; cin >> number; if (number > max) max = number;count = count + 1;}

Init counter to 0 while (count < n) // n is number of

times through loop { // all actions in

loop count = count + 1; }

Write a loop to find the min of 8 numbers

count = 0;min = 99999999;while (count < 8){cout << "Enter a number>

";

cin >> number; if (number < min) min = number;count = count + 1;}

Init counter to 0 while (count < n) // n is number of

times through loop { // all actions in

loop count = count + 1; }

Write code that validates user input for a letter (use isalpha)template:cout << "Enter a value> ";cin >> value;// vv1 .. vvn are all of the valid

valueswhile ((value != vv1) && …

(value != vvn)) {cout << "Your entry is

invalid."; cout << "Enter a " << vv1

<< ", " << … << "vvn> "; cin >> value; }

cout << "Enter a value> ";cin >> value;while (!isalpha(value)) {cout << "Your entry is

invalid."; cout << "Enter a letter> "; cin >> value; }

Review -- We know count-controlled loop, sentinel-

controlled loops, validation loops finding max or min in a series of

numbers

Need to know: how to do other common things in

loops

Accumlate data in loops sum = sum + newnumber; sum = sum + count; product = product + factor power = power * factor if (newnumber should replace

savedvalue) savedvalue = newnumber

Accumulation shortcuts count++ < -- > count = count + 1 ++count < -- > count = count + 1 can be part of another statement. count++ (postincrement) increment

done after the rest of the statement ++count (preincrement) more

efficient. done before the rest of the statement

More accumulation shortcuts total += value is the same as

total += value total -= decrement is the same as

total = total – decrement product = product * factor is the same as

product *= factor quotient /= divisor, remainder %= divisor is also legal

--stepdown, stepdown-- is same as stepdown = stepdown - 1

Lots of operators so far Look at precedence Note associativity

commaleft to right,

assignmentright to left= += -= *= /= %=

logical ORleft to right||

logical ANDleft to right&&

equalityleft to right== !=

relationalleft to right< <= > >=

insertion extraction

left to right<< >>

additiveleft to right+ -

multiplicativeleft to right* / %

unaryright to left++ -- (pre) + - !

unaryleft to right++ -- (post)

parensleft to right()

TypeAssociativityOperator

for loops mainly for count-controlled loops warning: i not visible outside loop

for (int i=0; i < nbrtimestoloop; ++i){// do processing}

while-for equivalence

for (int i=0; i < nbrtimestoloop; ++i)

{// do processing}

int i=0;while (i <

nbrtimestoloop){// do processing++i;}

Find min of 8 numbers -- forint count = 0;min = 99999999;while (count < 8){cout << "Enter a number>

";

cin >> number; if (number < min) min = number;++count;}

min = 99999999;for (int count =0; count

< 8; ++count){cout << "Enter a

number> ";

cin >> number; if (number < min) min = number;}

How to format code for loops indent statements within loop use { }s almost all of the time (not

always with for loops) put update at end of loop

Functions with Reference Parmeters

Sections 3.17, 3.10, 3.11

Parameter Reviewint getsmaller(int x, int y){ if (x>y) return y; else return x;}

int main{ int a=0, b=2, c; c = getsmaller(a, b);}

0 2

0 2

Use of functions function call

name of function, name of parameters no types use return value

function header and definition names and types of parameters return value type

function prototype types of parameters (names optional)

return value type

Names of Parameters

int getsmaller(int x, int y){ if (x>y) return y; else return x;}int main{ int a=0, b=2, c; c = getsmaller(a, b);}

formal parametersin function header

Actual parameters in function call

Write a program that reads 2 floats and calculates the largest, sum, and average. Write and use three functions: large2, sum2, average2. At least one of these functions should call another function.

Discuss your answer with 2 others.

#include <iostream>#include <cstdlib>

using namespace std;

float average2(float, float);float large2(float, float);float sum2(float, float);

int main(){ float a, b, average, larger, sum; cout << “Enter two numbers> ”; cin >> a >> b; average = average2(a, b); larger = large2(a, b); sum = sum2(a, b); cout << “The two integers are ” << a << “and ” << b << “. Their average is ” << average << “; the larger is ” << larger << “; the sum is ” << sum << “.” << endl; return EXIT_SUCCESS;}

float large2(float x, float y){ if (x > y) return x; else return y;}

float small2(float x, float y){ temp = large2(x, y); if (temp == x) return y;else return x;} float average2(float x, float y){ return (x+y)/2;}

Input Parmeters All of the parameters so far have had a

starting value that the function used. When the function was complete and

control returned to the caller, the value of the actual parameters had not changed:

y=4.0; sqrt(y) -- y is unchanged x=2.0; pow(y, x) -- x and y are unchanged

These are called input parameters (have a value at the beginning; that value is unchanged when function is done)

Non-input Parametersletter = getletter();

no parameters. reads and returns letter char

letter = toupper(letter);

one parameter. reads and puts letter char in the parameter

getletter(letter);


toupper(letter);

one parameter. letter has an initial value which is (may be) changed

Input, Output, Input-Output Parameters

letter = toupper(letter); // input parameter


getletter(letter); // output parameter


toupper(letter); // input-output parameter

one parameter. letter has an initial value which is (may be) changed

Value and Reference Parameters

Value parameters copy the value of the actual parameter to the value of the formal parameter

letter = toupper(letter); // input parameter

Reference parameters do NOT copy the value. Instead, the formal parameter is a pointer to the actual parameter

getletter(letter); // output parameter

Input parameters may be value; output, input-output parameters must be reference

Reference Parameters

& in function header and prototype no change to function call

void getletter(char&); // for prototypevoid getletter(char &letter) // for

headergetletter(myletter); for call

#include <iostream>#include <cstdlib>

using namespace std;

void toupper(char&);void getletter(char&);void printletter(char);

int main(){char c;getletter(c);toupper(c);printletter(c);return EXIT_SUCCESS;}

void toupper(char &c){ if ((c >= 'a') && (c <='z')) c -= 32; return; }

void getletter(char &c){ c = '0'; while (!isalpha(c))

{ cout << "please enter a letter (a-z)> "; cin >> c;}

}

void printletter(char c){ cout << "letter is " << c << endl;}

Trace Reference Parameters

Your turn

Write a program to sum the number from 1 to 10. Use a function Sum

which has two parameters, the current number and the

currentsum. When the function returns, the sum has been

incremented by the current number.

Discuss your answer with 2 others.

File streams

Chapter 14.2-14.6, 12.1-12.4, 12.6-12.8

Remember redirection? It lets you read from a file

prompt> a.out <infile >outfile

We have substituted the disk file infile for the standard input file (keyboard)

and outfile for the standard output file (display)

Redirection isn't enoughWhat if we wanted to read from more than

one file at the same time? student registration file

prepare bill -> tuition bill

student info file

File Streams It’s really not much different than

using cin and cout. Why call it a STREAM?

All devices can be viewed simply as a stream of chars (like a river is a stream of water) whether it is an input or output stream.

How to use file streams Include <fstream> Declare input files as ifstream Declare output files as ofstream To read in, use >> To write out use << Keep going until eof is reached

#include <fstream>

#include <iostream>

#include <string>

#include <cstdlib>

int main()

{

const char * filename=”myfile.txt";

string word;

ifstream wordfile(filename);

if (!wordfile) // check to see if file is there.

{cout << "Error: no file name " << filename << endl;

return EXIT_FAILURE;

}

int count=0;

while (wordfile >> word) // keep going until eof.

{

cout << "Word is " << word << endl;

count++;

}

wordfile.close();

cout << "the number of words in the file is " << count << endl;

return EXIT_SUCCESS;

}

Using an output file The same as modifications to

input; instead of cout, use filename

make sure you format check for problems opening (file

will be erased if there)

Passing file streams as parameters Always pass as reference type is ifstream or ofstreamvoid getnextword(ifstream&, string&);

getnextword(infile, word);

void getnextword(ifstream &infile, string &word){ if (!infile.eof())

infile >> word;}

Write your own Write a program that reads word

from a file, writes them to a duplicate file, and counts the number of words. Use a function, writeword, which has two parameters, the file to be written to and the word being written (an input parameter)

More stream functions open, get, put, eof, fail, close

put and get are used for reading files a char at a time

THEY DO NOT SKIP SPACES etc! You can use cin type input ( >> ) but it

skips white space.Remember how cin does the same?

cerr, section 12.2.3 What if you wanted to output an error but

the person was redirecting the output to a file?

prompt> a.out >outfile

YOU WOULDN'T SEE THE ERROR! the cerr stream is a special kind of output

which would NOT be redirected to the standard output device.

cerrOriginal program that reads in words and printed

them to the screen could redirect output and produce the same results as second. But if you want to see errors no matter what, use cerr:

if (!wordfile) // check to see if file is there. {

cerr << "Error: no file name " << filename << endl; return EXIT_SUCCESS; }

Output manipulators a function called as though it were

being output, e.g., endl setw, precision, showpoint, scientific,

fixed can be used on any output stream, cout

or file some defined in iostream; some in

iomanip (those with parameters)

Output Manipulators

{float x;cout << setw(10) << x << endl;} endl we've seen setw(10) minimum of 10 spaces (x, like

all output is right justified)

Output flags

float x;cout << fixed << precision(2) << x << endl; or:

cout.setf (ios::fixed);cout.precision(2);cout << "x" << endl;

Output flags/manipulators Lots of them:

right, left, internal fill, setfill hex, octal, dec, showbase uppercase scientific, fixed, showpoint precision showposI will not expect you to memorize these for a

test; know they exist so you can look them up as needed

Input functions (get) get (can use with cin or any input stream)

cin.get(ch); // puts char in output parameter ch = cin.get() // returns the char as function

value cin.get(chararray, maxsize, <delimiter>)

// null character inserted into array as terminator

// null character remains in input stream// works like getline

Input functions getline (with cin or any input stream)

null character inserted in array at end delimiter read and discarded (UNLIKE get) cin.getline(chararray, size, <delimiter>)

member of istream class getline(istream, string, <delimiter>)

string is of string class. NO dot notation

More input functions ignore

istream.ignore(); // skips over one char istream.ignore(n); // skips over n chars istream.ignore(n, '?'); // skips over n chars, or

until a question mark whichever is first' examples:

cin.ignore(); ifstream ins; ins.ignore(1000, '\n'); // throw away next

return

Arrays

Chapter 4

What can't we do with single variables?

Sort 10 numbersint x,y,z,m,n,o,p,q, r,s;largest = x; if (y > x) largest = y;if (z > x) largest = z; … then get second largest, third largest, etc. To get 2nd largest, have largest, but no way

to say "n was the largest, so don’t look at n anymore"

what if 10,000 numbers?

Use arrays blocks of storage with many

elements all of the same kind char chararray[10];

'3''?' 'e''K''a' 'W' 'X' ' ' '0' 'R'

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chararray

' ''3'‘a'

chararray[0] = 'R';

Accessing Elements in Arrays

'3''?' 'e''K''a' 'W' 'X' ' ' '0' 'R'

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chararray

'e''?' 'e''K''R' 'W' 'X' 'R''Z'

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chararray

chararray[3] = chararray[4];

int i=8; chararray[i] = 'Z';

‘0'‘e'

More accessing elements

'3''?' 'e''K''a' 'W' 'X' ' ' '0' 'R'

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chararray

// NOTE: no chararray[10]. runtime array index out //of bounds error

chararray[3] = chararray[4] + 1; // 'e' + 1 == 'f'

'f''?' 'e''K''a' 'W' 'X' ' ' '0' 'R'

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chararray

Array Overview element can be of any type (int, char,

bool, float, string) all elements the same type indexes always integers starting at 0 range of index is 0 – (size-1) can (should) have constant as a size

int arraysize = 10; // same as char chararray[10];

char chararry[arraysize];

Integer Arraysconst int arraysize = 10;int myarray[arraysize];myarray[0] = 3;myarrary[3] = 2;

myarray[myarray[3]] = 15;

myarray[myarray[3] + 4] = myarray[0];

myarray[myarray[3]+myarray[4]] = 63;

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myarray

23 315

myarray[4] = 1;

163

Arrays in loops

myarray[0] = 0; myarray[1] = 0;myarray[2] = 0; myarray[3] = 0;myarray[4] = 0; myarray[5] = 0;myarray[6] = 0; myarray[7] = 0;myarray[8] = 0; myarray[9] = 0;ORfor ( int i=0; i< arraysize; ++i) myarray[i] = 0;

Your Turn Trace myarray[i] = 0 loop, then write: Write values for myarray

without a loop with a loop

Read values for myarray without a loop with a loop

Sum values in myarray without a loop with a loop

Array initialization

int x[10] = {3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

int x[] = {3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

int x[10] = {3, 4, 5, 6, 7}; // index5-9 are 0

int x[5] = {3, 4, 5, 6, 7, 8, 9, 10, 11, 12}; // syntax error

Array Elements as Parameters

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myarray

3 2 315 63

• function call accesses individual elements using []s (like assign, etc. for individual elements:

•swap(myarray[3], myarray[5]);

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myarray

3 63 315 2

Passing Array Elements as Parameters Prototype and Function Definition

Works as though the elements were not in an array (they're not in the definition)

prototype: void swap(int&, int&); // & for input/output. NO []s!!! definition – same as our previous swap

void swap(int &x, int&y){int temp; temp = x; x = y; y = temp;}

Passing Arrays as Parameters: Function Prototypes Arrays are passed by reference. no

choice. no & (not true for array values – e.g., void swap(int&, int&);

MUST have [ ]s. Do not include size void writearray(int[], int);

if array is not changed, use const void writearray(const int[], int);

no &,but stillpassed

byreference

Passing Arrays as Parameters:Function Definitions

void writearray(const int x[], int size) {for (int i=0;i<size;++i) cout << "Element " << i << " is " << x[i] << endl; }

no size, no &.Does have [ ]s

Passing Arrays as Parameters:Function Calls

int main(){ const int arraysize = 10; int myarray[arraysize]; readarray(myarray); // NO [ ]! writearrary(myarray);}

Your Turn Write a program that reads in 10

integers, swaps the first and last, the second and second to last, the third and third to last, and the fourth and fourth to last (reverses the array). Write the reversed array out. Use functions swap, readarray, writearray.

Character Arrays as Strings Array elements can only be

accessed individually, not as a whole: cin >> myarray; // is illegal

Want to be able to think of character arrays as all one chunk, e.g., "Hello"

'l''l' 'o''e''H' '\0' 'X' ' ' '0' 'R'

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chararray

Character arrays as Strings: \0

• '\0' is a string terminator in a character array:

•cout << myarray will not work (if myarray is an integer array).

•cout << chararray WILL print "Hello" IF a '\0' terminator is there

•With '\0', you can cin and cout char arrays as chunks treating them like strings.

'l''l' 'o''e''H' '\0' 'X' ' ' '0' 'R'

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chararray

Writing and Testing Programs

Drivers and StubsSupplement to text

Write and Test Parts Do not write entire programs at a time Write the whole algorithm in English,

pseudo-code Choose which part to implement Write that part Test that part Write another part (in another file).

Test that part When done with all parts, integrate all

parts (in one or many files)

How do I write one part? Choose a function to write Type it into a file (algorithm is

already written) Write a main section to test just

that function Compile and test

What about main? Write main Instead of writing each function,

have “stubs” – functions with the correct prototype, header and return type (can be a constant), but don’t do any calculation

Compile and Test main

Example

Write a program that prints the product of the absolute value of 2 integers. Each of the 2 integers will be calculated by reading in 3 integers and choosing the largest (so a total of 6 integers will be entered).

Write the algorithm – NOT C++

Algorithm

1. Read in 3 numbers2. Get the largest of those. Call it a.3. Get the absolute value of a. call it absa4. Read in 3 more numbers. 5. Get the largest of those. Call it b.6. Get the absolute value of b. Call it

absb7. Output the product of absa and absb

Algorithm (more detailed)1. Read in 3 numbers

Could have a separate function, but this is short, and we don’t know how to write a function to do this yet.

cin >> int1 >> int2 >> int3 (with labels)

2. Get the largest of those. Call it a. We’ll call this function max3. Takes 3

integers as parameters. Returns the largest.

3. Get the absolute value of a. call it absa We’ll call this function abs (already written in

some math library, but we’ll write out own).

Algorithm (continued)4. Read in 3 more numbers.

cin >> int1 >> int2 >> int3 (ok to call the same names as earlier)

5. Get the largest of those. Call it b. Call max3: b = max(int1, int2, int3)

6. Get the absolute value of b. Call it absb

Call abs: absb = abs(b)

7. Output the product of absa and absb cout << absa * absb (with labels)

Next First, write and test max3.cc Second, write and test abs.cc Third, write and test main Fourth, after all is tested, modify

main to use max3, abs, and test

Writing the functions

Write the algorithm for function max3.

Algorithm for max3

Now, write the function prototype and function definition.

1. Compare int1 and int2. Store larger in largest

2. Compare largest and int3. Store larger in largest

3. Return largest

Write prototype and definition for max3prototype:int max3(int, int, int);

max3 (in file max3.cc)

int max3(int int1, int int2, int int3){ int largest; if (int1 < int2) largest = int2;else largest = int1; // if int1 > or = to int2if (int3 > largest) largest = int3;return largest;

}

Test max3 Write a driver main function whose sole purpose

it to test a function calls the function with reasonable

values (input w/cin or constants – advantage of cin is you can run multiple tests)

prints the return value.

max3 driver#include <iostream>#include "max3.cc"

using namespace std;int max3(int, int, int);

int main(){ int int1, int2, int3; cout << “Enter 3 integers to test max3> "; cin >> int1 >> int2 >> int3; cout << "The result of max3 called with " << int1 << ", " << int2 ", " << ", and " << int3 << " is " << max3(int1, int2, int3) << endl;}

Write algorithm for abs

1. if input parameter (x) is positive, return x

2. otherwise, return x * -1

Write prototype and definition for absprototype: int abs(int);

definition in file abs.cc:int abs(int x){ if (x >= 0) return x; else return x*-1;}

Write driver to test abs#include <iostream>#include "abs.cc"using namespace std;int abs(int);int main(){ int x; cout << "Enter an integer to test abs> "; cin >> x; cout << "abs called with " << x << " returns " << abs(x) << endl;}

Write main function (algorithm below)

1. Read in 3 numberscin >> int1 >> int2 >> int3 (with labels)

2. Get the largest of those. Call it a. Call max3.

3. Get the absolute value of a. call it absa Call abs

4. Read in 3 more numbers. cin >> int1 >> int2 >> int3

5. Get the largest of those. Call it b. Call max3: b = max(int1, int2, int3)

6. Get the absolute value of b. Call it absb Call abs: absb = abs(b)

7. Output the product of absa and absb cout << absa * absb (with labels)

#include <iostream>// do NOT include max and absusing namespace std;int abs(int);int max(int, int, int);int main(){int int1, int2, int3, a, b, absa, absb; cout << "Enter three integers> "; // 1 cin >> int1 >> int2 >> int3; a = max3(int1, int2, int3); // 2// next cout debugging only cout << "Result of max3 call is: " << a << endl;absa = abs(a); // 3// next cout for debugging onlycout << "result of abs is " << absa << endl;

cout << "Enter three more integers> "; // 4

cin >> int1 >> int2 >> int3; b = max3(int1, int2, int3); // 5// next cout debugging only cout << "Result of max3 call is: " << b <<

endl;absb = abs(b); // 6// next cout for debugging onlycout << "result of abs is " << absb << endl;cout << "The answer is " << absa * absb

<< endl; // 7} // end main

int max3(int a, int b, int c){ cout << "in abs with parameters " << a << ", " << b

<< ", " << c < end; return 10;}

int abs(int x){ cout << "in x with parameter " << x << endl;

return x;}

Next First, write and test max3.cc Second, write and test abs.cc Third, write and test main Fourth, after all is tested, modify

main to use max3, abs, and test

Write the entire program modifying main and including max3 and abs

#include <iostream>include "abs.cc"include "max3.cc" using namespace std;int abs(int);int max(int, int, int);int main(){int int1, int2, int3, a, b, absa, absb; cout << "Enter three integers> "; // 1 cin >> int1 >> int2 >> int3; a = max3(int1, int2, int3); // 2// cout << "Result of max3 call is: " << a << endl;absa = abs(a); // 3// cout << "result of abs is " << absa << endl;cout << "Enter three more integers> "; // 4 cin >> int1 >> int2 >> int3; b = max3(int1, int2, int3); // 5// cout << "Result of max3 call is: " << b << endl;absb = abs(b); // 6//cout << "result of abs is " << absb << endl;cout << "The answer is " << absa * absb << endl; // 7} // end main

CPSC 230 Computers and Programming I

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