Introduction to C++ Programming

Introduction to C++

Programming

Engr. Muniba DCSE UET Peshawar

Contents of Week 02

• Data types, Constants

• Floating Point Constants, Size, Memory Concepts

• Names, Keywords, Identifiers

• Declaration and Definition of Variables • A Simple Program: Printing a Line of Text

3

Introduction to C++ Programming

• C++ language

– Facilitates structured and disciplined approach to computer program design

• Following several examples

– Illustrate many important features of C++ – Each analyzed one statement at a time • Structured programming

A Simple C++ Example

// C++ simple example

#include <iostream> //for C++ Input and Output int main ()

{

int number3;

std::cout << "Enter a number:"; std::cin >> number3;

int number2, sum;

std::cout << "Enter another number:"; std::cin >> number2;

sum = number2 + number3;

std::cout << "Sum is: " << sum <<std::endl; return 0;

standard output stream object stream insertion operator

stream extraction operator standard input stream object

stream manipulator

5

Important Parts of a C++ program

• Comments:

• Preprocessor directives :

• Function

– Body of the function – Return statement

Comments

• A comment is descriptive text used to help a reader of the program understand its content.

• Explain programs to other programmers

– Improve program readability

• Ignored by compiler • Single-line comment

– Begin with // – Example

• //allows program to output data to the screen.

• Multi-line comment

– Start with /* – End with */

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Preprocessor Directives

• Preprocessor directives

– Processed by preprocessor before compiling – Begin with #

– Example

• #include <iostream>

– Tells preprocessor to include the input/output stream header file <iostream>

• White spaces

– Blank lines, space characters and tabs

– Delimiter, used to make programs easier to read – Extra spaces are ignored by the compiler

Function main

• A part of every C++ program

– Exactly one function in a program must be main – main is a Keyword.

• Keyword : A word in code that is reserved by C++ for a specific use.

• Header of function main : int main( ) • Body is delimited by braces ({ })

9

Statements

• Instruct the program to perform an action • All statements end with a semicolon (;) • Examples :

– return 0;

return

_Statement

• Because function main() returns an integer value, there must be a statement that indicates what this value is. • The statement return 0 ;

– indicates that main() returns a value of zero to the operating system.

– The value 0 indicates the program terminated successfully – greater than 0 means an error

– maybe a different number for a different error

– if declare our function as int and don't use return will get a warning from the compiler

• One of several means to exit a function • Used at the end of main

Namespaces

• Namespace: a generalization of scope.

• C++ allows access to multiple namespaces with the ' :: ' operator

• A namespace lets us distinguish between two names from different places

• In C++ the standard library is in the std namespace

• Things in no namespace are said to be in the

How to use a namespace

std::cout << "Hello";

– Specify that this cout object is from the std namespace

using namespace std;

– Copy everything from the std namespace into the global namespace

using std::cout;

– Copy cout from the std namespace into the global namespace

What about <iostream.h>

• Very similar to <iostream>

• Also declares cin, cout and endl

– In the global namespace not in the std namespace

• This is for compatibility with older versions of C++

Output Statement (1)

std::cout << “Welcome to C++!\n”;

– std::cout

• Standard output stream object.

• Defined in input/output stream header file <iostream>

• We are using a name (cout) that belongs to “namespace” std. • Normally outputs to computer screen.

– Stream insertion operator <<

• Value to right (right operand) inserted into left operand.

• The string of characters contained between “ ” after the operator << shows on computer screen.

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Output Statement (2)

• Escape character : backslash : "\"

• Escape sequence : A character preceded by backslash (\)

– Indicates “special” character output – Examples :

• "\n"

– Newline. Cursor moves to beginning of next line on the screen

• “\t”

Good Programming Practices

• Add comments

– Every program should begin with a comment that describes the purpose of the program, author,

date and time.

• Use good indentation

– Indent the entire body of each function one level within the braces that delimit the body of the

function. This makes a program’s functional

structure stand out and helps make the program easier to read.

 2003 Prentice Hall, Inc. All rights reserved.

17

1 // Fig. 1.2: fig01_02.cpp 2 // A first program in C++.

3 #include <iostream> // Preprocessor Directive 4

5 // function main begins program execution 6 int main()

7 {

8 std::cout << "Welcome to C++!\n"; 9

10 return 0; // indicate that program ended successfully 11

12 } // end function main

Welcome to C++!

A Simple Program:

Printing a Line of Text

Escape Sequence Description

\n Newline. Position the screen cursor to the

beginning of the next line.

\t Horizontal tab. Move the screen cursor to the next

tab stop.

\r Carriage return. Position the screen cursor to the

beginning of the current line; do not advance to the next line.

\a Alert. Sound the system bell.

\\ Backslash. Used to print a backslash character.

\" Double quote. Used to print a double quote character.

 2003 Prentice Hall, Inc. All rights reserved.

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1 // Fig. 1.4: fig01_04.cpp

2 // Printing a line with multiple statements. 3 #include <iostream>

4

5 // function main begins program execution 6 int main()

7 {

8 std::cout << "Welcome "; 9 std::cout << "to C++!\n";

10

11 return 0; // indicate that program ended successfully 12

13 } // end function main

Welcome to C++!

A Simple Program: Printing a Line of Text

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1 // Fig. 1.5: fig01_05.cpp

2 // Printing multiple lines with a single statement

3 #include <iostream> 4

5 // function main begins program execution

6 int main()

7 {

8 std::cout << "Welcome\nto\n\nC++!\n"; 9

10 return 0; // indicate that program ended successfully

11

12 } // end function main

Welcome to

C++!

A Simple Program: Printing a Line of Text

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Input stream object

• std::cin from <iostream>

– Usually connected to keyboard – Stream extraction operator >>

• Waits for user to input value, press Enter (Return) key • Stores value in variable to right of operator

– Converts value to variable data type

– Example

• int number1;

• std::cin >> number1;

– Reads an integer typed at the keyboard – Stores the integer in variable number1

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1 // Fig. 1.6: fig01_06.cpp

2 // Addition program.

3 #include <iostream>

4

5 // function main begins program execution

6 int main()

7 {

8 int integer1; // first number to be input by user

9 int integer2; // second number to be input by user

10 int sum; // variable in which sum will be stored 11

12 std::cout << "Enter first integer\n"; // prompt

13 std::cin >> integer1; // read an integer

14

15 std::cout << "Enter second integer\n"; // prompt

16 std::cin >> integer2; // read an integer

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18 sum = integer1 + integer2; // assign result to sum

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20 std::cout << "Sum is " << sum << std::endl; // print sum

21

22 return 0; // indicate that program ended successfully

Enter first integer 45

Enter second integer 72

Sum is 117

Another Simple Program: Adding Two Integers

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Memory Concepts

• Variable names

– Correspond to actual locations in computer's memory

• Every variable has name, type, size and value

– When new value placed into variable, overwrites old value

• Writing to memory is destructive

– Reading variables from memory nondestructive – Example

• sum = number1 + number2;

– Value of sum is overwritten

Fig.1| Memory location showing the name and value of variable number1.

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Fig. 2| Memory locations after storing values for number1 and number2.

Fig. 3 | Memory locations after calculating and storing the sum of number1 and number2.

age.cpp

cout << "I am " << age << " years old" << endl;

age++; /* add one */

cout << "Next year I will be " << age << endl; return 0;

Statements

cout << "I am " << age << " years old" << endl;

Statement Block

• List of instructions

• Everything between ‘{’ and ‘}’

(curly brackets, braces)

#include <iostream>

using namespace std;

int main()

{

int age=26;

cout << "I am " << age << " years old" << endl; age++; /* add one */

cout << "Next year I will be " << age << endl; return 0;

Functions

• One of the building block of the C++ program.

#include <iostream>

using namespace std;

int main()

{

int age=26;

cout << "I am " << age << " years old" << endl;

age++; /* add one */

Data Types

• int, float, void, unsigned int, long, double, char • string, list, …

• Ways to represent information

#include <iostream>

using namespace std;

int main() {

int age=26;

cout << "I am " << age << " years old" << endl;

age++; /* add one */

cout << "Next year I will be " << age << endl; return 0;

Data Type: Char

• Size : Single byte • Range: -128 : 127

• Hold one character such as ‘a’ or ‘A’ • Variable declaration: char ch;

Data Type: int

• Size: 2 bytes

• Range: -32768 : 32767

• Holds the integer value specified in the range • Type long or long int

• Size: 4 bytes

Data Type: float

• Size: 4 bytes

• Range: 10e-38 : 10e38 with 6 digits of precision

• Holds the numbers that have fractional part e.g., 12.55

Data Type: double

• Size: 8 bytes

• Range: 10e308 : 10e-308

• Holds floating point numbers with 15 digits of precision

• Type: long double

void datatype

• Special data type to represent nothing or an unknown type of data

• int main(void)

– main function expects nothing – Exactly the same as int main()

• void main()

– main function returns nothing

Keywords

 Sometimes called reserved words.

 Are defined as a part of the C++ language.  Reserved for specific purpose

 Have special meaning and is known by compiler  Can not be used for anything else!

 Examples:

 char, int, float, void, signed, if, while, case, else  class, public, friend, this, operator, new, true

Keywords

cout << "I am " << age << " years old" << endl;

age++; /* add one */

cout << "Next year I will be " << age << endl; return 0;

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Keywords

• Cannot be used as identifiers or variable names

C++ Keyw o rd s

Keywords common to the C and C++ programming languages

auto break case char const

continue default do double else

enum extern float for goto

if int long register return

short signed sizeof static struct

switch typedef union unsigned void

volatile while

C++ only keywords

asm bool catch class const_cast

delete dynamic_cast explicit false friend

inline mutable namespace new operator

private protected public reinterpret_cast

static_cast template this throw true

try typeid typename using virtual

Constants

• Constant is a fixed value that does not change during the execution of the program.

• Divided into two types

– Numeric Constants

Numeric Constants

• Numbers are referred to as Numeric Constants • Consists of

– Numeric digits 0-9

– Plus (+) or Minus (-) sign

– If no sign by-default it is assumed to be positive – Decimal point

– No commas or blanks are allowed

• Examples – 30 – -500 – 3.14159 – 0.25432 – +100

Numeric Constants

• Represented in three ways

– Integer constant

– Floating-point constant – Exponential real constant

Integer Constant

• The numeric constant that doesn’t contain a decimal point

• Can be positive or negative • Examples – 70 – +134 – 0 – -500 – 7

Floating-Point Constants

• The numeric constants that does contain the decimal point

• Can be either positive or negative • Examples

– 0.3

– -56.34

Exponential Real Constants

• Floating point constant in the E-notation form. • Widely used in scientific & engineering

applications.

• Used to represent very small or very large numbers • Examples – 1.23E+2 – 1.0E3 – 8.8E-6 – 3.33E-2

Non-Numeric Constants

• Used for non-numeric purposes

• To produce output reports, headings, or printing messages

• Divided into two types

– Character Constants – String Constants

Character Constants

 Singular!

 One character defined character set.

 Surrounded on the single quotation mark.

 All the alphabetic, numeric and special characters can be

character constants except backslash and the single quotation mark.  Examples:  ‘A’  ‘a’  ‘$’  ‘4’ ‘\\’ for backslash

String Constants

 A sequence characters surrounded by double

quotation marks.

 Considered a single item.  Examples:

 “UMBC”

 “I like ice cream.”  “123”

 “CAR”

Names

 Sometimes called identifiers.  Words that are not reserved.

 User defined words or the programmer supplied

names

 Can be of any length, but on the first 31 are

significant (too long is as bad as too short).

 Are case sensitive:

 abc is different from ABC

 Must begin with a letter and the rest can be

Identifiers

– age, height, i, j, x, y, cout

• Also function names

– main #include <iostream> using namespace std; int main() { int age=26;

cout << "I am " << age << " years old" << endl;

Variables

• Specific storage location in memory where value can be stored

• A value, which may vary during program execution.

• A variable is the name used to represent a piece of information.

Declaration & Definition of Variables

• All the variables must defined and declared before usage.

• Declaration introduces a variable’s name into a program

• If the declaration also set aside memory for the variables it is called the definition

• Variables can be assigned a value at the time of declaration

Declaration statements

string user_name;

float height, weight;

int age=26;

string user_name="Matt";

Algorithms

• Computing problems

– Solved by executing a series of actions in a specific order

• Algorithm a procedure determining – Actions to be executed

– Order to be executed – Example: recipe

• Program control

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Pseudocode

• Pseudocode

– Artificial, informal language used to develop algorithms

– Similar to everyday English

• Not executed on computers

– Used to think out program before coding

• Easy to convert into C++ program

– Only executable statements