User Defined Functions in C

C Functions:

A function is defined as a block of code that is used to perform some specific task.

In functions, we use flower brackets ({}) which contain the set of programming statements. The main purpose of using functions is we can reuse and modularise our programs. In the C program, we can call a function multiple times. In other words, we can say that the collection of functions creates a program.

Types of Functions:

In C, programming functions are of two types

1. Library Functions:
   Library functions are built-in functions directly declared in C header files and placed in a common location called a library. such as scanf(), printf(), gets() etc. All functions have some specific task to be performed.
   scanf () – used to get the input from the user
   printf () – used to print the output to the screen
2. User-defined Functions:
   User-defined functions are the functions that are created by the user, and the user can reuse them multiple times. A user-defined function mainly has three components
   • Function declaration
   • Function call
   • Function definition

Function Declaration:

Always a function is declared in the global section or globally in a C program. It specifies the compiler about the function name, function parameter, etc.

Syntax:

Return type function name( type1 argument1, type2 argument2, …);

Function Call:

We can call our function throughout the program anywhere. We must always remember that the parameters must be the same as the function declaration. If there are two parameters, then in the function call also, there must be two parameters.

Syntax:

functionname(argument1, argument2, …);      

Different Aspects of Function Calls:

There are four different function protocol styles present in C programming.

• With parameters and with return values (WPWR)

Example:

//program for finding factorial using Functions with parameter and return value
#include < stdio.h >
#include < conio.h >
int factorial( int x );
void main(void)
{
int n, f;
clrscr();
printf( “Enter n value:” );
scanf( “%d”, &n );
f = factorial(n);
printf(“The factorial of %d is %d”, n, f);
}
int factorial ( int x )
{
int fact = 1, i;
if( x== 0 )
{
return fact;
}
else
{
for( i = x; i>=1; i-- )
{
Fact = fact *I;
}
return fact;
}
}

Output:

Enter n value: 4
The factorial of 4 is 24

Explanation:

Firstly, we have included stdio for standard input and output, conio to clear the output screen. We have taken the protocol style wpwr ( with parameter and with return value ). After that, we declared a function with return type int. In the main method, we have declared two variables, n (to store the given input) and f (to store the result after the function call). We have called the function, and the output will be stored in the variable f. After the function call, the program will redirect to the function body, and the operation will be done there. Once the operations are done, it will return the result to the main method from where it has been called. The 4 factorial is (4*3*2*1 = 24). So the output will be printed as 24.

• With parameter and without return value (WPWOR)

Example:

//program for finding factorial using Functions with parameter and without return value
#include< stdio.h >
#include< conio.h >
Void factorial(int x);
void main(void)
{
int n;
clrscr();
printf( “Enter n value:” );
scanf( “%d”, &n );
factorial(n); 
}
void factorial ( int x )
{
int fact = 1, i;
if( x== 0 )
{
printf(“Factorial of %d is %d:”, x, fact);
}
else
{
for( i = x; i>=1; i-- )
{
Fact = fact *I;
}
printf(“The factorial of %d is %d”, x, fact);
}
}

Output:

Enter n value: 5
The factorial of 5 is 120

Explanation:

Here we have used the protocol style WPWOR(with parameter and without return value). If we are using without return values, we must give the return type as void( it will not return anything). So we directly print the output in the function body. And the factorial of 5 is (5*4*3*2*1 = 120). So the output will be printed as “The factorial of 5 is 120”.

• Without parameter and With return values (WOPWR)

Example:

//program for finding factorial using Functions without parameter and with return value
#include < stdio.h >
#include < conio.h >
int factorial( void );
void main(void)
{
int f;
clrscr();
f = factorial();
printf(“The factorial is %d”, f);
}
int factorial( void )
{
int x, fact = 1, i;
printf(“enter the value of x:”);
scanf(“%d”, &x);
if( x == 0 )
{
return fact;
}
else
{
for(i = x;i>=1;i--)
{
fact = fact*I;
}
return fact;
}
}

Output:

Enter the value of x: 8
The factorial is 40320

Explanation:

Here we have used the protocol style WOPWR (without parameter and with return value). If we are using without parameters, we do not pass any parameters. So, we directly declare the variables in the function body. And return the result to the function call. The factorial of 8 is (8*7*6*5*4*3*2*1 = 40320). So, the output will be printed as “The factorial is 40320”.

• Without parameter and without return value (WOPWOR)

Example:

//program for finding factorial using Functions without parameters and without return value
#include < stdio.h >
#include < conio.h >
Void factorial( void );
Void main( void )
{
clrscr();
factorial();
}
Void factorial( void )
{
int x, fact = 1, i;
printf(“enter the value of x:”);
scanf(“%d”, &x);
if(x == 0)
{
Printf(“The factorial of %d is %d”, x, fact);
}
else
{
for( i=x;i>=1;i--)
{
fact = fact *i;
}
Printf(“The factorial of %d is %d”, x, fact);
}
}

Output:

Enter the value of x: 6
The factorial of 6 is 720

Explanation:

Here we have used the protocol style WOPWOR (without parameter and without return value). If we are using without parameters and return values, we must give the return type as void (it will not return anything), and we will not give any parameters. So, we directly declare the variable and print the output in the function body. And the factorial of 6 is (6*5*4*3*2*1 = 720). So, the output will be printed as “The factorial of 6 is 720”.

Function Definition:

This block is more important in functions because all the executable statements are written here. When we call the function, it will be redirected to function definition (function body ). After all the operations, it will return only one value.

Syntax:

return type function name(argument 1, argument 2, argument 3, ….){function body;}

Advantages of Functions:

• By using functions, we can divide a complex problem into small blocks.
• We can call the function anywhere in the program and any number of times.
• Using functions, we can avoid writing of same code again and again in the program.
• The Main purpose of using functions is we can reuse the code/reusability of the code in the programs.