Introduction to C++

2.12.1The Parts of a C++ Program

–Anatomy of a simple C++ program

The Parts of a C++ The Parts of a C++ ProgramProgram

// sample C++ program

#include <iostream>

using namespace std;

int main()

{

cout << "Hello, there!";

return 0;

}

preprocessor directive

comment

which namespace to use

beginning of function named main

beginning of block for mainoutput statement

end of block for main

string literalsend 0 to operating system

Hello, there!

A different exampleA different example

// sample C++ program

#include <iostream>

using namespace std;

int main ()

{

int a, b = 1;

a = b + b++;

printf ("%d\n", a);

return 0;

}

preprocessor directive

comment

which namespace to use

beginning of function named main

beginning of block for main

output statement

end of block for main

send 0 to operating system

variable declaration

Increment and Addition operations

2

Special CharactersSpecial CharactersCharacter Name Meaning

// Double slash Beginning of a comment

# Pound sign Beginning of preprocessor directive

< > Open/close brackets Enclose filename in #include

( ) Open/close parentheses

Used when naming a function

{ } Open/close brace Encloses a group of statements

" " Open/close quotation marks

Encloses string of characters

; Semicolon End of a programming statement

/* */ Slash * Comment

2.22.2The cout Object

The The coutcout Object ObjectDisplays output on the computer

screen

You use the stream insertion operator << to send output to cout:

cout << "Programming is fun!";Programming is fun!

The The coutcout Object ObjectCan be used to send more than

one item to cout:

cout << "Hello " << "there!";Or:

cout << "Hello ";cout << "there!";

Hello there!

The The coutcout Object ObjectThis produces one line of output:

cout << "Programming is ";cout << "fun!";

Programming is fun!

The The endlendl Manipulator ManipulatorYou can use the endl manipulator to

start a new line of output. This will produce two lines of output:

cout << "Programming is" << endl;cout << "fun!";

Programming isfun!

The The endlendl Manipulator Manipulator

cout << "Programming is" << endl;cout << "fun!";

Programming isfun!

The The endlendl Manipulator ManipulatorYou do NOT put quotation marks

around endl

The last character in endl is a lowercase L, not the number 1.

endl This is a lowercase L

The The \n \n Escape SequenceEscape SequenceYou can also use the \n escape

sequence to start a new line of output. This will produce two lines of output:

cout << "Programming is\n";cout << "fun!";

Notice that the \n is INSIDE

the string.

The The \n \n Escape SequenceEscape Sequence

cout << "Programming is\n";cout << "fun!";

Programming isfun!

Escape Sequence for use Escape Sequence for use with output (cout)with output (cout)

Escape Sequence

Name Meaning

\n Newline Cursor to go to next line for printing

\t Horizontal tab Cursor to go to next tab stop

\a Alarm Computer to beep

\b Backspace Cursor to back up or left one position

\r Return Cursor to start of current line

\\ Backslash Print backsplash

\’ Single quote Print quotation mark

\” Double quote Print double quotation

cout with variablescout with variables

int number;

number = 10;

cout << “The number is “ << number << endl;

The number is 10

Only pass variable name, no quotes around it

2.32.3The #include Directive

The The #include#include Directive DirectiveInserts the contents of another file

into the programThis is a preprocessor directive, not

part of C++ language#include lines not seen by compiler#include lines ARE seen by

preprocessorDo not place a semicolon at end of #include line (this is syntax you just have to remember)

Recall the Preprocessor ….Recall the Preprocessor ….a) Create file containing the program

with a text editor.b) Run preprocessor to convert source

file directives to source code program statements.

c) Run compiler to convert source program into machine instructions.

d) Run linker to connect hardware-specific code to machine instructions, producing an executable file.

Steps b–d are often performed by a single command or button click.

Errors detected at any step will prevent execution of following steps.

Compiled Languages

Example #includeExample #includeHere we include iostream which has

the cout object in it This is the input-output stream library. iostream is a header file

// sample C++ program

#include <iostream>

using namespace std;

int main()

{

cout << "Hello, there!";

return 0;

}

preprocessor directive

The preprocessor will insert ATthis point in the code the entire contents of iostream header file atthis point of the program. Its contents include the definition of cout object

Where is this file iostream???---answer the <> around it tells the preprocessor it is in a standard location. This is typically downloaded and installed for you when you install C++ (typically there will be an /include directory somewhere in install)

#include <filename> versus #include <filename> versus #include “/path/filename.h”#include “/path/filename.h”#include <filename>

◦ Looks in the IDE C++ devloper tools standard include directories that were created at install time for the file.

#include “/path/filename.h”◦ Looks for the filename.h file in the /path/ directory

path.◦ Used when you are creating your own files (we will

learn later how to do) OR when you have downloaded some 3rd party non-standard C++ header files.

We will see more about thislater in the course

2.42.4Variables and Literals

Variables and LiteralsVariables and LiteralsVariable: a storage location in

memory

◦Has a name and a type of data it can hold

◦Must be defined before it can be used:

int item;

int = type and stands for integeritem = variable name

Variable Definition in Variable Definition in Program 2-7Program 2-7

Variable Definition

Variables can change Variables can change valuevalue

int item; item = 2; item = 99;

CHANGING the value of item from2 to 99

What can variables be What can variables be used for?used for?Store Information a User might type inStore information from a fileStore information from a database your program

needs to operateStore information representing system information

(i.e. ask the date, time, o.s. info, call system functions and get results)

Store information from calculations (from data above or generated—i.e. a timer)

Store information given to it from another programStore information from other machines/services

across network/internet/webMore….

LiteralsLiteralsLiteral: a value that is written

into a program’s code.

"hello, there" (string literal)12 (integer literal)

99.33 (floating point literal)

Integer Literal in Program Integer Literal in Program 2-92-9

20 is an integer literal

String Literals in Program String Literals in Program 2-92-9

These are string literals

QuestionQuestionWhat kind of literal is “5” ?

Answer = a string (NOT a number)

2.52.5Identifiers

IdentifiersIdentifiersAn identifier is a programmer-

defined name for some part of a program: variables, functions, etc.

C++ Key WordsC++ Key Words

You cannot use any of the C++ key words as an identifier. These words have reserved meaning.

This means (in general) you should not use these as variable names

Variable NamesVariable NamesA variable name should represent the

purpose of the variable. For example:

itemsOrdered

The purpose of this variable is to hold the number of items ordered.

But it could also have the meaning of holding a list of the items that were ordered. Is there a better variable name? How about numItemsOrdered?

Notice the conventionstart with lower case letter and then as chaintogether words for meaning start of each wordis capitalizede.g. dogListor currentTime

Identifier RulesIdentifier RulesThe first character of an identifier

must be an alphabetic character or and underscore ( _ ),

After the first character you may use ONLY alphabetic characters, numbers, or underscore characters.

Upper- and lowercase characters are distinct (this means U is different than u) This is called case sensitive.

Valid and Invalid Valid and Invalid IdentifiersIdentifiers

IDENTIFIER VALID? REASON IF INVALID

totalSales Yes

total_Sales Yes

total.Sales No Cannot contain .

4thQtrSales No Cannot begin with digit

totalSale$ No Cannot contain $

2.62.6Integer Data Types

Integer Data TypesInteger Data Types

• Integer variables can hold whole numbers such as 12, 7, and -99.

Wait a minute???Wait a minute???int and long look the same?

◦4 bytes with same range

Well, this can be implementation dependent. ◦i.e. on 32 bit window machines it long is 4

bytes but, on some Unix machines it can be 8 bytes.

So –what we really know is sizeof(long) >= sizeof(int) >= 4 bytes

Why did this happen?Original int was intended tobe the “natural” word size ofa processor…but, nowmany modern processors have changed and can holddifferent word sizes

Defining VariablesDefining VariablesVariables of the same type can be defined

- On separate lines:int length;int width;unsigned int area;

- On the same line:int length, width;unsigned int area;

Variables of different types must be in different definitions

Integer Types in Program Integer Types in Program 2-102-10

This program has three variables: checking, miles, and days

Integer LiteralsInteger LiteralsAn integer literal is an integer

value that is typed into a program’s code. For example:

itemsOrdered = 15;

In this code, 15 is an integer literal.

Integer Literals in Program Integer Literals in Program 2-102-10

Integer Literals

Here we are initializing the variables to literal values

Integer LiteralsInteger LiteralsInteger literals are stored in

memory as ints by defaultTo store an integer constant in a

long memory location, put ‘L’ at the end of the number: 1234L

Constants that begin with ‘0’ (zero) are base 8: 075

Constants that begin with ‘0x’ are base 16: 0x75A

2.72.7The char Data Type

The The charchar Data Type Data TypeUsed to hold characters or very

small integer values i.e. greyscale images have each pixel

represented by 8 bits of information

Usually 1 byte of memoryNumeric value of character from

the character set is stored in memory:CODE:

char letter;letter = 'C';

MEMORY:letter

67

Character LiteralsCharacter LiteralsCharacter literals must be

enclosed in single quote marks. Example:

'A'

Character Literals in Program Character Literals in Program 2-132-13

Character StringsCharacter StringsA series of characters in consecutive

memory locations:"Hello"

Stored with the null terminator, \0, at the end:

Comprised of the characters between the " "

H e l l o \0

2.82.8The C++ string Class

The C++ The C++ stringstring Class ClassSpecial data type supports working

with strings #include <string>Can define string variables in

programs:string firstName, lastName;

Can receive values with assignment operator:firstName = "George";lastName = "Washington";

Can be displayed via coutcout << firstName << " " << lastName;

Remember this means thereis a string header file in a standard/include directory that was installed

The The stringstring class in Program class in Program 2-152-15

2.92.9Floating-Point Data Types

Floating-Point Data TypesFloating-Point Data TypesThe floating-point data types are:floatdoublelong double

They can hold real numbers such as:12.45 -3.8

Stored in a form similar to scientific notation

All floating-point numbers are signed

Floating-Point Data TypesFloating-Point Data Types

Remember our discussion about the size of long and int ---- this applies here for double and long double

Floating-Point LiteralsFloating-Point LiteralsCan be represented in

◦Fixed point (decimal) notation:31.4159 0.0000625

◦E notation:3.14159E1 6.25e-5

Are double by defaultCan be forced to be float

(3.14159f) or long double (0.0000625L)

Floating-Point Data Types in Floating-Point Data Types in Program 2-16Program 2-16

2.102.10The bool Data Type

The The boolbool Data Type Data TypeRepresents values that are true

or false

bool variables are stored as small integers

false is represented by 0, true by 1:

bool allDone = true;

bool finished = false;

allDone finished

1 0

true andfalse are C++keywords

Boolean Variables in Program Boolean Variables in Program 2-172-17

2.112.11Determining the Size of a Data Type

Determining the Size of a Determining the Size of a Data TypeData Type

The sizeof operator gives the size of any data type or variable:double amount;

cout << "A double is stored in "

<< sizeof(double) << "bytes\n";

cout << "Variable amount is stored in "

<< sizeof(amount)

<< "bytes\n";sizeof is afunction in C++

2.122.12Variable Assignments and Initialization

Variable Assignments and Variable Assignments and InitializationInitializationAn assignment statement uses

the = operator to store a value in a variable.

item = 12;

This statement assigns the value 12 to the item variable.

AssignmentAssignmentThe variable receiving the value

must appear on the left side of the = operator.

This will NOT work:

// ERROR! 12 = item;

Variable InitializationVariable InitializationTo initialize a variable means to

assign it a value when it is defined:

int length = 12;

Can initialize some or all variables:int length = 12, width = 5, area;

Variable Initialization in Variable Initialization in Program 2-19Program 2-19

Declaring Variables With the Declaring Variables With the autoauto Key Key WordWord

C++ 11 introduces an alternative way to define variables, using the auto key word and an initialization value. Here is an example:

auto amount = 100;The auto key word tells the compiler to

determine the variable’s data type from the initialization value.

auto interestRate= 12.0;

auto stockCode = 'D';

auto customerNum = 459L;

int

double

char

long

2.132.13Scope

ScopeScopeThe scope of a variable: the part

of the program in which the variable can be accessed

A variable cannot be used before it is defined

Variable Out of Scope in Variable Out of Scope in Program 2-20Program 2-20

Can’t use a variablebefore it is declared

2.142.14Arithmetic Operators

Arithmetic OperatorsArithmetic OperatorsUsed for performing numeric

calculationsC++ has unary, binary, and

ternary operators:◦unary (1 operand) -5

◦binary (2 operands) 13 - 7

◦ternary (3 operands) exp1 ? exp2 : exp3

operand = arguments or items that the operating is operating on.-5 here the operand is 513 – 7 here the operands are 13 and 7Exp1 ? Exp2 : exp3 here the operands are exp1,exp2 and exp3

Binary Arithmetic Binary Arithmetic OperatorsOperators

SYMBOL OPERATION EXAMPLE VALUE OF ans

+ addition ans = 7 + 3; 10

- subtraction ans = 7 - 3; 4

* multiplication ans = 7 * 3; 21

/ division ans = 7 / 3; 2

% modulus ans = 7 % 3; 1

remember binary here means 2 operands

Arithmetic Operators in Arithmetic Operators in Program 2-21Program 2-21 here we are using the *, multiplication operator

and +, the addition operator

A Closer Look at the A Closer Look at the // OperatorOperator

/ (division) operator performs integer division if both operands are integerscout << 13 / 5; // displays 2cout << 91 / 7; // displays 13

If either operand is floating point, the result is floating pointcout << 13 / 5.0; // displays 2.6cout << 91.0 / 7; // displays 13.0

A Closer Look at the A Closer Look at the %% OperatorOperator% (modulus) operator computes

the remainder resulting from integer division

cout << 13 % 5; // displays 3

% requires integers for both operands

cout << 13 % 5.0; // error

2.152.15Comments

CommentsCommentsUsed to document parts of the

programIntended for persons reading the

source code of the program:◦Indicate the purpose of the program◦Describe the use of variables◦Explain complex sections of code

Are ignored by the compiler

Single-Line CommentsSingle-Line Comments

Begin with // through to the end of line:int length = 12; // length in inchesint width = 15; // width in inchesint area; // calculated area

// calculate rectangle areaarea = length * width;

Multi-Line CommentsMulti-Line CommentsBegin with /*, end with */Can span multiple lines:/* this is a multi-line comment*/

Can begin and end on the same line:int area; /* calculated area */

Comment Guidelines – how Comment Guidelines – how muchmuchFor you, a beginning

programmer, I suggest MORE is better

Explain algorithms, formulas, variables that you are using

Explain with enough detail that someone who did NOT write the code and is a beginning programmer could understand it

Comment Guidelines --Comment Guidelines --wherewhereTowards the top of your programBefore every function you createBefore loops and test conditionsNext to declared variables.

2.162.16Named Constants

Named ConstantsNamed ConstantsNamed constant (constant

variable): variable whose content cannot be changed during program execution

Used for representing constant values with descriptive names:const double TAX_RATE = 0.0675;const int NUM_STATES = 50;

Often named in uppercase letters

Named Constants in Program Named Constants in Program 2-282-28

2.172.17Programming Style

Programming StyleProgramming StyleThe visual organization of the

source codeIncludes the use of spaces, tabs,

and blank linesDoes not affect the syntax of the

programAffects the readability of the

source code

Programming StyleProgramming StyleCommon elements to improve

readability:Braces { } aligned verticallyIndentation of statements within

a set of bracesBlank lines between declaration

and other statementsLong statements wrapped over

multiple lines with aligned operators

2.182.18Standard and Prestandard C++

Standard and Prestandard Standard and Prestandard C++C++Older-style C++ programs:

◦Use .h at end of header files:◦ #include <iostream.h>◦Use #define preprocessor directive

instead of const definitions◦Do not use using namespace

convention◦May not compile with a standard C+

+ compiler

#define#define directive in Program directive in Program 2-312-31