Post on 01-Jan-2016
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Agenda
Review C++ Standard Numeric Types
Arithmetic–way more than you want!
Character (char) data type
For Loop
Syntax, Run-time and Logical Errors
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Review:Standard Program Structure
To solve most problems, your main() program will generally look like this (conceptually)
1. Declare variables for input, result and intermediate data
2. Ask for data (cout)3. Input data (cin)4. Calculate result5. Output result (cout)
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An interactive C++ program://circle.cpp Calculate area of a circle// given a radius value#include <iostream>using namespace std;int main(){ int area, radius;cout << "enter a radius: ";cin >> radius;area = radius * radius * 3.14;cout << "the area is " << area << endl;
return 0;}
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A small problem…
Run circle.cpp:
But according to our code, it should be 3.14
What happened?
enter a radius: 1
the area is 3
Press any key to continue . . .
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We used the wrong data type!
Go back, change:
int area, radius;
To:
float area, radius;
Now it works…the lesson?
1) Data types are important!
2) Testing is important!
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Agenda
Review
C++ Standard Numeric Types Arithmetic–way more than you want!
Character (char) data type
For Loop
Syntax, Run-time and Logical Errors
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Basic C++ Data Types
int – Represents integers
float – Represents real (floating point) numbers
char – Represents characters (single letters)
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Integers only store whole numbers
int a=4; // puts 4 in a
int a=4.579132; // puts 4 in a
INTS are great for loop counters, representing inventory, numbers of “things”
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Trivia—other integer types
uses range of values
short..............(2 bytes)….-32,767 to 32767
long …….….(4 bytes)…-2 bill to +2 billion
int ………….(depends)…long (sometimes short)
unsigned short (2 bytes)…0 to 65535
unsigned long ...(4 bytes) …0 to 4 billion
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Beware Integer wraparound
// wrap.cpp
int a, b, c;
a = 2000000000;
b = 2 * a;
c = 3 * a;
cout << "b is " << b << endl;
cout << "c is " << c << endl;
b is -294967296
c is 1705032704
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FLOATING-POINT Types
float is used to represent numbers with a
fractional part such as 2.543 or 6.45 etc…
or really big numbers that won’t fit inside ints
uses range precision
float...........(4 bytes)……10-38 to 1038……..6 digits
double…...(8 bytes)……10-308 to 10308…...15 digits
long double (10 bytes)....10-4932 to 104932…19 digits
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What does floating point mean?
Consider a number like 123.45
“Float” the point so that all the digits are on its right
(here the point is shifted 3 digits to the left)
123.45 = 0.12345 x 10 3
E-notation: the letter ‘e’= “x10 to the power of”
You can actually enter or display data using ‘e’:
123.45 same as 0.12345e3 same as 1.2345e2
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Fine…. How is this stored in a float variable ??
The mantissa .12345 and the exponent 3 are stored separately (in a variable)
For a 32 bit float type :
23 bit mantissa + 8 bit exponent + 1 sign bit
For a 64 bit double type :
52 bit mantissa + 11 bit exponent + 1 sign bit
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Implications for Accuracy(round-off error)
A float only stores about 6 digits of mantissafloat PI=3.1415926535897932384626;PI really contains 3.14159float x=50000000000000.0, y=10000.0;x=x+y; DOES NOT CHANGE X!!! (no room)
Use a double if you need more precisiondouble PI=3.141592653589793;About 16 digits of mantissadouble x=50000000000000.0, y=10000.0;x=x+y; DOES CHANGE X!!! (now there’s room)
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Q1) Practice your Scientific Notation (answers at end of slides)
1234.56 = ____________ x 10 ____
.03413= ____________ e ____
6.78 x 107 = ____________
5.32e-5 = ____________
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Displaying Floating Point data
cout << 4.5 << endl;cout << -.375 << endl;cout << 10.6666666 << endl;cout << 67800000.0 << endl;cout << 523000000000 << endl;cout << 523000000000. << endl;cout << 0.000098 << endl;
Output
4.5
-0.375
10.6667
6.78e+07
3308957184
5.23e+11
9.8e-05
This is an integer, no ‘.’
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Formating Floating Point Outputcout<<fixed<<showpoint<<setprecision(2);
cout << 4.5 << endl;cout << -.375 << endl;cout << 10.6666666 << endl;cout << 67800000.0 << endl;cout << 523000000000 << endl;cout << 523000000000. << endl;cout << 0.000098 << endl;
You can use this on problem 8
Output
4.50
-0.38
10.67
67800000.00
3308957184
523000000000.00
0.00
For this to work, #include<iomanip>
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Constants are “variables” -- that never change
Use the keyword “const” in front of declaration
You MUST provide initial value at declarationconst double PI=3.141592653589793;
const double METERS_PER_YARD = 0.9144;
const int MAX=1000;
Now you can say: area = PI * radius * radius;
Don’t over do it: const int SECONDS_PER_MINUTE = 60;
You can use a constant for problem 7
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Agenda
Review
C++ Standard Numeric Types
Arithmetic–way more than you want! Character (char) data type
For Loop
Syntax, Run-time and Logical Errors
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Arithmetic in C++
Basic operations + - * /
Math formulas need to be converted into C++ syntax:
FORMULA Equivalent C++A = r2 area=3.14*radius*radius;
F = (v -a) force=(v-a)/(v+a);
(v+a)
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Arithmetic -- Order of Precedence
* and / are done first, then + and –Equal levels are done left to rightExample:
3 * 4 + 2 = 142 + 3 * 4 = 146 + 4 / 2 + 3 = 6 + 2 + 3 =
8 + 3 = 11
Parentheses have highest precedence (use if you want different order)
(6 + 4) / (2 + 3) = 2
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Q2) Practice Arithmetic Precedence
Evaluate the following
1+2 * 3 + 4 = _______
5 + 6 / 2 * 3 = _______
1 + 2 * (3 + 4) = _______
(7 + 5) / (2 * 3) = _______
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Mixed-type Expressions
Expressions involving int and float will give a result of type float (the most inclusive type)
Suppose you have
int n; float x;
Then
n + x results in float
n * 4 results in int
n + 4.0 results in double (4.0 is double)
(default for floating pt literals)
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Mixed-type Assignments
Assigning int to float is perfectly safe
Assigning float to int may lose fractional partSuppose you have
int n; float x;
Then
1. x = 15; stores 15 in x
2. n = 4.5; stores 4 in n -- Compiler Warning!
To satisfy the compiler for (2.) simply explain
your intentions: n = int(4.5);
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Q3) Can you guess what is stored in these variables?
int m, n; double x,y;
m = 3.0;
n = 12.7;
x = m;
x = x + 0.5
m = m + 1;
y = x + 1;
m n x y
? ? ? ?
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Integer Division
CAUTION—this is a common C++ error
When both sides are int, the result MUST be int
9 / 2 = 4 9 / 10 = 0
Sometimes this is what we want (convert inches to inches and feet)
Usually causes programming errors
When one side is float, the answer is float9 / 2.0 = 4.5 9.0 / 10 = 0.9
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Q4) Can you guess what is stored in these variables?
int m, n; double x,y;
m = 10 / 3;
n = 30 / 7;
x = n * m;
y = 3 / 4 * x;
y = x * 3 / 4;
y = (x + 3) / 4;
m n x y
? ? ? ?
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One more thing…type-casting
If you want to perform floating point division on a pair of integer variables, you can…but you have to temporarily convert one of them to float first:
int m=3, n=4; float y;y = float(m) / n; ( y = 0.75)
WRONGy = float(m/n); ( y = 0)
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Break Time!
Download Lab2MoreBasics.cpp
Work on problems 1-4, 7,8
Call me over if you have questions
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Remainder % operator
The expression 10 / 3 gives the quotient, 3
We use 10 % 3 to get the remainder, 1
4 / 3 = 1 12 % 6 = 0
4 % 3 = 1 13 % 6 = ____
2 / 3 = 0 14 % 6 = ____
2 % 3 = 2 23 % 7 = _____
Only use % on integers
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What good is % operator?You can use it to subdivide something into hierarchical units:
int feet, inches;cout << "Enter inches: ";cin >> inches;feet = inches / 12;inches = inches % 12;cout << feet << " ft. " << inches << " in.";
This is used in things like time, weight, length, change, etc.
Use this slide on Problem 9
Enter inches: 75
6 ft. 3 in.
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Arithmetic Assignment Operators
Numeric operators +, -, *, /, % can be combined with the assignment operator =
Saves time and typing
Only when you want to store result in one of operands
a += b a = a + b
a -= b a = a - b
a *= b a = a * b
a /= b a = a / b
a %= b a = a % b
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Q5) Arithmetic Assign Operator Table START: int x=0;
Shorthand Same as Result
x+=5;
x*=2;
x/=5;
x-=2;
x+=10;
x*=3;
x%=8
x/=5;
x=x+5;
x=x*2;
x=x/5;
x=x-2;
5
10
2
0
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Agenda
Review
C++ Standard Numeric Types
Arithmetic–way more than you want!
Character (char) data type For Loop
Syntax, Run-time and Logical Errors
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CHARACTER types (see Lab3-1)
char……………... (1 byte)
unsigned char…….(1 byte)
A char stores a single letter
What is actually stored is the binary sequence corresponding to a letter’s ASCII code
You can either store a letter, or the numeric code for the letter in a char
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Check this out….#include <iostream.h>void main(){ both a and c contain 65 or ‘A’char a = 65, c = 'A'; cout << “ c = “ << c << endl;cout << “ a = “ << a << endl;}Output…..c = Aa = A (in other words, ‘A’ is same as 65)
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Character InputRead 2 chars
char grade1, grade2;cin>>grade1>>grade2;cout<<“Grade 1 is ”<<grade1<<endl;cout<<“Grade 2 is ”<<grade2<<endl;NOTE• white space ignored: type AB, A B, A (enter)
B same result• Another interesting topic, character escape and
control sequences, p 53/54
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Agenda
Review
C++ Standard Numeric Types
Arithmetic–way more than you want!
Character (char) data type
For Loop Syntax, Run-time and Logical Errors
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Bored with single execution programs?
Add a for loop to repeat your code several times:for (int k=1; k<=final_value; k=k+1)
{
statements to repeat
}
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Example Looped code
Add a for loop to repeat your code several times:int main(){ for (int k=1; k<=3; k=k+1) {
cout<<“Testing”<<k<<endl; }}
Testing 1
Testing 2
Testing 3
Or k++ for short
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Example Application (for challenge)
Calculate pay for 3 employees: int hrs; double rate;
for (int emp=1; emp<=3; emp++)
{
cout<<“Enter hours & rate: ”;
cin>> hrs>> rate;
cout<<“Pay = $”<< hrs * rate <<endl;
}
See p57 to let user determine the number of iterations
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Agenda
Review
C++ Standard Numeric Types
Arithmetic–way more than you want!
Character (char) data type
For Loop
Syntax, Run-time and Logical Errors
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Types of ErrorsSyntax: an error in your C++ language/grammar (covered last week)
confuses compiler (The dog his paw)forgetting a ; misspelling a variable name datha=3.14;
Runtime: when you do something illegal during program execution temp=0.0;rate=1.0/temp; // dividing a number by zero –crash!
Logical (or Semantic): When you say something illogical A paw ate his dog. ( Good grammar, illogical
meaning) avg = b + c / 2;
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Tracking them down
Syntax—double click on error message,
it takes you to line of code
Look at or above that line for possible errors
Runtime & LogicalYou detect them by checking output against test plan
Pinpoint them by displaying variables during intermediate steps (cout)
OR Use debugger to step through program, put watch on variables
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LIST OF KEYWORDS…..asmautoboolbreakcasecatchcharclassconstconst_castcontinue
defaultdeletedodoubledynamic_
castelseenumexplicitexportextern
false
floatforfriendgotoifinlineintlongmutablenamespace
newoperator
private protectedpublicregisterreinterpret
_castreturnshortsignedsizeofstatic
static_caststructswitchtemplatethisthrowtruetrytypedeftypeidtypenameunionunsignedusing
virtualvoid
volatilewchar_twhile
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That’s a wrap !
What we learned today:Data Types
Rules of Arithmetic
For loops
How to debug your program
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A1) Answers to Scientific Notation
1234.56 = 1.23456 x 103
.03413= 3.413 e -2
6.78 x 107 = 67800000
5.32e-5 = 0.0000532
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A2) Arithmetic Precedence
Evaluate the following
1+2 * 3 + 4 = 11
5 + 6 / 2 * 3 = 14
1 + 2 * (3 + 4) = 15
(7 + 5) / (2 * 3) = 2
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A3) Answer:
int m, n; double x,y;
m = 3.0;
n = 12.7;
x = m;
x = x + 0.5
m = m + 1;
y = x + 1;
m n x y
? ? ? ?
3
12
3.0
3.5
4
4.5
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A4) Integer Division
int m, n; double x,y;
m = 10 / 3;
n = 30 / 7;
x = n * m;
y = 3 / 4 * x;
y = x * 3 / 4;
y = (x + 3) / 4;
m n x y
? ? ? ?
3
4
12
0
9
3.75