C++ Function or Methods

Function:

• A function is a set of instructions that are used to perform specified tasks that repeatedly occur in the main program.
• It helps to avoid duplication of work and also breaks down a large program into a number of small functions.
• It is used to divide the complex task into a manageable task.
• Functions are classified into two types as shown below,

              * User-defined functions
              * Pre-defined functions

1.User-defined function:

• The users have full scope to implement their own ideas in the function.
• It defined by the users according to their requirements are called user-defined functions.
• Elements of user-defined function:

               * Function declaration
               * Function definition
               * Function call

Syntax of user-defined function:

<Header_files>

Main_function()

{

variable_declaration;

//function declaration part

return_type or data_type function_name(parameters list);

// function calling part

function_name();//no parameter passed

or

function_name(parameter);//parameter passed

or

return value=function_name(parameter);

//printing statements

}

//function definition part

Data_type function_name(parameters list)

{

Local variable declaration;

......

Body of the function;

return (expression);

}

Parameters:

• It provides data communication between the calling function and the called function.
• There are two types of parameters,

    (i). Actual parameters:

• Used in data transferred from the main function to the user-defined function.

    (ii). Formal parameters:

• Used in data transferred from a user-defined function into the main function.

For example:

Where

          a, b are the actual parameters.

          x,y is the formal parameters.

Local and global variables:

Local variable:

• The local variables are defined within the body of the function.
• This variable used within the function only, other functions can not access these variables.

Example:

fun1(int a, int b)

{

          int c,d;

}

Global variable:

• The global variables are defined outside the main () function, multiple functions can use these variables.

Example:

int x,y=10;

main()

{

          int a,b;

}

Example program for local and global variables.

#include<iostream.h>

#include<conio.h>

int i; //Global variable

void main()

{

          int j; //Local variable

void fun1();//Function declaration

i=0;

clrscr();

cout<<"\n Value of i in main function: "<<i;

fun1();//Function calling

cout<<"\n Value of i in after call: "<<i;

getch();

}

//Function definition

void fun1()

{

int k; //Local variable for fun1()

i=50;

}

Output:

The return statement:

• A return statement is an optional part of the function.
• It is used to populate the results without any printing function.

Syntax:

return; or return(expression);

Example:

if(x>0)

          return(1);

else

          return(0);

Function calling:

• A function can be called by specifying the function name in the source program with parameters if presence within parentheses.
• If a function is not declaring the variable to return, we must be specified the data type at the return value.

For example:

• It is divided into two types,

1.Function call without a parameter:

#include<iostream.h>

#include<conio.h>

void main()

{

msg_func();//Function definition without parameter and

                          called the function

cout<<"\n Message from main program or function");

getch();

}

//Function definition

msg_func()

{

clrscr();

          cout<<"\n Message from msg_func() user defined function";

}

Output:

2.Function call with parameter:

#include<iostream.h>

#include<conio.h>

void main()

{

int a;

clrscr();

a=msg_func(10,20);//Function definition with parameter and 

                                   called the function

cout<<"\n Message from main program or function";

cout<<"\n The value of a is : "<<a;

getch();

}

//Function definition

int msg_func(int x,int y)

{

int z;

z=x+y;

cout<<"\n Message from msg_func() user defined function";

return(z);

}

Output:

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