C++ Tutorial

C++ Program Structure

Let us look at a simple code that would print the words Hello World.

#include <iostream>
using namespace std;

// main() is where program execution begins.

int main()
{
   cout << "Hello World"; // prints Hello World
   return 0;
}

Let us look various parts of the above program:

• The C++ language defines several headers, which contain information that is either necessary or useful to your program. For this program, the header <iostream> is needed.
• The line using namespace std; tells the compiler to use the std namespace. Namespaces are a relatively recent addition to C++.
• The next line // main() is where program execution begins. is a single-line comment available in C++. Single-line comments begin with // and stop at the end of the line.
• The line int main() is the main function where program execution begins.
• The next line cout << "This is my first C++ program."; causes the message "This is my first C++ program" to be displayed on the screen.
• The next line return 0; terminates main( )function and causes it to return the value 0 to the calling process.

Data Types

The following table shows the variable type, how much memory it takes to store the value in memory, and what is maximum and minimum value which can be stored in such type of variables.

Type	Typical Bit Width	Typical Range
char	1byte	-127 to 127 or 0 to 255
unsigned char	1byte	0 to 255
signed char	1byte	-127 to 127
int	4bytes	-2147483648 to 2147483647
unsigned int	4bytes	0 to 4294967295
signed int	4bytes	-2147483648 to 2147483647
short int	2bytes	-32768 to 32767
unsigned short int	Range	0 to 65,535
signed short int	Range	-32768 to 32767
long int	4bytes	-2,147,483,648 to 2,147,483,647
signed long int	4bytes	same as long int
unsigned long int	4bytes	0 to 4,294,967,295
float	4bytes	+/- 3.4e +/- 38 (~7 digits)
double	8bytes	+/- 1.7e +/- 308 (~15 digits)
long double	8bytes	+/- 1.7e +/- 308 (~15 digits)
wchar_t	2 or 4 bytes	1 wide character

C++ Keywords

The following list shows the reserved words in C++. These reserved words may not be used as constant or variable or any other identifier names.

asm	else	new	this
auto	enum	operator	throw
bool	explicit	private	true
break	export	protected	try
case	extern	public	typedef
catch	false	register	typeid
char	float	reinterpret_cast	typename
class	for	return	union
const	friend	short	unsigned
const_cast	goto	signed	using
continue	if	sizeof	virtual
default	inline	static	void
delete	int	static_cast	volatile
do	long	struct	wchar_t
double	mutable	switch	while
dynamic_cast	namespace	template

Variable

A variable provides us with named storage that our programs can manipulate.

DataType variableName1, variableName2,…variableNameN;

int i;      // declared but not initialised
char c;
int i, j, k;  // Multiple declaration

int i=10;         //initialization and declaration in same step
int i=10, j=11;

If a variable is declared and not initialized by default it will hold a garbage value. Also, if a variable is once declared and if try to declare it again, we will get a compile time error.

Loop

A loop statement allows us to execute a statement or group of statements multiple times and following is the general from of a loop statement in most of the programming languages.

There are 3 type of loops in C++ language

while loop

while loop can be address as an entry control loop. It is completed in 3 steps.

Variable initialization.( e.g int x=0; )

condition( e.g while( x<=10) )

Variable increment or decrement ( x++ or x-- or x=x+2 )

Syntax 

variable initialization ;

while (condition)

{

 statements ;

 variable increment or decrement ; 

}

For loop

For loop is used to execute a set of statement repeatedly until a particular condition is satisfied. we can say it an open ended loop. General format is,

for(initialization; condition ; increment/decrement)

{

  statement-block;

}

Nested for loop

We can also have nested for loop, i.e one for loop inside another for loop. Basic syntax is,

for(initialization; condition; increment/decrement)

{

  for(initialization; condition; increment/decrement)

     {

        statement ;

     }

}

do while loop

In some situations it is necessary to execute body of the loop before testing the condition. Such situations can be handled with the help of do-while loop. do statement evaluates the body of the loop first and at the end, the condition is checked using while statement.

General format of do-while loop is,

do

{

 ....

 .....

}

while(condition)

The Infinite Loop

A loop becomes infinite loop if a condition never becomes false. 

C++ programmers more commonly use the for(;;) construct to signify an infinite loop.

#include <iostream>
using namespace std;

int main ()
{

for( ; ; )
   {
      printf("This loop will run forever.\n");
   }

return 0;
}

Decision making in C++

Decision making is about deciding the order of execution of statements based on certain conditions or repeat a group of statements until certain specified conditions are met. C++ handles decision-making by supporting the following statements,

Simple if statement

The general form of a simple if statement is,

if( expression )
{
 statement-inside;
}
 statement-outside;

If the expression is true, then 'statement-inside' it will be executed, otherwise 'statement-inside' is skipped and only 'statement-outside' is executed.

if...else statement

The general form of a simple if...else statement is,

if( expression )
{
 statement-block1;
}
else
{
 statement-block2;
}

If the 'expression' is true, the 'statement-block1' is executed, else 'statement-block1' is skipped and 'statement-block2' is executed.

Nested if....else statement

The general form of a nested if...else statement is,

if( expression )
{
  if( expression1 )
   {
     statement-block1;
   }
  else
   {
     statement-block 2;
   }
}
else
{
 statement-block 3;
}

if 'expression' is false the 'statement-block3' will be executed, otherwise it continues to perform the test for 'expression 1' . If the 'expression 1' is true the 'statement-block1' is executed otherwise 'statement-block2' is executed.

else-if ladder

The general form of else-if ladder is,

if(expression 1)
{
 statement-block1;
}
else if(expression 2)
{
 statement-block2;
}
else if(expression 3 )
{
 statement-block3;
}
else

 default-statement;

The expression is tested from the top(of the ladder) downwards. As soon as the true condition is found, the statement associated with it is executed.

Functions in C++

Functions are used to provide modularity to a program. Creating an application using function makes it easier to understand, edit, check errors etc.

Syntax of Function

return-type function-name (parameters)

{
// function-body
}

• return-type : suggests what the function will return. It can be int, char, some pointer or even a class object. There can be functions which does not return anything, they are mentioned with void.
• Function Name : is the name of the function, using the function name it is called.
• Parameters : are variables to hold values of arguments passed while function is called. A function may or may not contain parameter list.
• Function body : is he part where the code statements are written.

Call by Value

In this calling technique we pass the values of arguments which are stored or copied into the formal parameters of functions. Hence, the original values are unchanged only the parameters inside function changes.

Call by Reference

In this we pass the address of the variable as arguments. In this case the formal parameter can be taken as a reference or a pointer, in both the case they will change the values of the original variable.

Array

C++ provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type.

An array is a sequence of variable that can store value of one particular data type.

type array_name[size];

int age[5];

This array can hold 5 integer elements.

C++ Multidimensional Arrays

C++ allows programmer to create array of an array known as multidimensional arrays. Consider this example:

int x[3][4];

Here, x is a two dimensional array. This array can hold 12 elements. You can think this array as table with 3 row and each row has 4 column.

String in C++

String is a sequence of characters. 

The standard C++ library provides a string class type that supports wide range of functions that manipulate null-terminated strings.

strcpy(s1, s2)

Copies string s2 into string s1.

strcat(s1, s2)

Concatenates string s2 onto the end of string s1.

strlen(s1)

Returns the length of string s1.

strcmp(s1, s2)

Returns 0 if s1 and s2 are the same; less than 0 if s1<s2; greater than 0 if s1>s2.

strchr(s1, ch)

Returns a pointer to the first occurrence of character ch in string s1.

strstr(s1, s2)

Returns a pointer to the first occurrence of string s2 in string s1.