User defined function in C programming language

We will learn about User defined function in the C programming language.

C programming language allows coders to define functions to perform special tasks. As functions are defined by users, they are called user-defined functions.

user-defined functions have contained the block of statements which are written by the user to perform a task

Elements of user-defined function in C

the function has three related elements, in order to establish the function

Function declaration
function call
Function definition

Here is an example to find the sum of two numbers. a user-defined function sumNum() is created to perform this task

#include <stdio.h>
#include <stdlib.h>
int sumNum(int x,int y); //function declaration
int main()
{
    int i,j,sum;
    printf("Please enter 2 numbers for find sum\n");
    scanf("%d %d",&i,&j);
    sum=sumNum(i,j); //function call
    printf("The result of sum is :%d",sum);
    getch();
    return 0;
}
int sumNum(int x, int y)//function definition
{
    int result;
result=x+y;
return result; //return statements
}

When the above code is compiled and executed, it produces the following results

Please enter 2 numbers for find sum
34
45
the result of sum is :79

we will discuss user-defined function using the above example

Declaration

declaration of the user-defined function.

A function declaration is a frame (prototype)of function that contains the function’s name, list of parameter and return type and ends with the semicolon. but it doesn’t,t contain the function body

Syntax

return_Type function_Name(parameter1,parameter2,......);

Example

Example of the function declaration

int  sum_Num(int x, int y,.........);

In the above example, int sumNum(int x, int y); is a function declaration which contains the following information

Every function declaration must contain the following 3 parts and ends with the semicolon in C language

function name – name of the function is sumNum()
return type – the return type of the function is int
arguments – two arguments of type int are passed to the function

Calling a function

Syntax

function_Name(Argument list);

Example

sum_Num(argument_1, argument_2,.......);

When the function is called, the control flow of the program move to function definition and statements executes the inside body of the function

Function Definition

The function definition is an expansion of function declaration. It contains codes in the body part of the function for execution program by the compiler – it contains the block of code for the special task

The syntax of the function definition

return_Type function_name(parameter_1, parameter_2,....){
//statements
//body of the function
}

The passing argument to a function

In the function of C programming language, when we called the function it used to passed value to the variable referred by argument. Above the program x,y are contained two parameters in the function and i,j are arguments of the function

In the above example, two variable i,j passed during the function call for passed arguments in the function definition.

When we passed an argument to the function, type of argument to the function and list of formal parameters must be matched. it is not, the compiler will throw an error

return statements

Return statements terminate the execution of the function and return value to calling the function. Also, return statements control of the program control and moved to the calling function.

Syntax

return (expression);

Example

return (result);
return (x+y);

In every function, function definition should be followed by the prototype of function declaration, if it is not, the compiler throws an error of the program.

Program 1

#include <stdio.h>
#include <stdlib.h>
int division(int x,int y); //function declaration or prototype
int main()
{
    int i,j,div;
    printf("Please enter 2 numbers for division\n");
    scanf("%d%d",&i,&j);
    div=division(i,j); //function call
    printf("The result of division is :%d",div);
    getch();
    return 0;
}
int division(int i, int j)
{
    int result;
result=i/j;
return result; //return statements
}

When the above code is compiled and executed, it produces the following results

Please enter 2 numbers for division
45
9
The result of division is :5

Types of the user-defined function in C language

User defined function in C can be categorized into four types:

function with no return value and without argument
function with no return value and with an argument
function with a return value and without argument
function with a return value and with an argument

Function with no return value and without argument

Add two numbers using the function

Program 1

#include <stdio.h>
#include <stdlib.h>
void add();
int main() {
    add();
    getch();
    return 0;
    }
    void add() {
        int a=10;
        int b=12;
        int c=a+b;
        printf("Total value of(a+b) is :%d\n",c); }

When the above code is compiled and executed, it produces the following results

Total value of(a+b) is : 22

Program 2

using get input method from user

#include <stdio.h>
#include <stdlib.h>
void add();
int main()
{
    add();
    getch();
    return 0;
}
void add()
{
    int a,b;
    printf("Enter your first number for a :");
    scanf("%d",&a);
    printf("Enter your first number for b :");
    scanf("%d",&b);
    int c=a+b;
    printf("Total value of(a+b) is :%d\n",c);
}

When the above code is compiled and executed, it produces the following results

Enter first number for a
12
Enter second number for  b
23
total number (a+b) is 35

In the above program, add() function take input from the user find total value and displays result on the screen – No argument passed and no return value

Function with no return value and with the argument

Find the difference between the two numbers using the function

Program 1

#include <stdio.h>
#include <stdlib.h>
void main()
{
diff(25,15);//calling function with arguments
getch();
    return 0;
}
void diff(int a,int b)//argument is passed to this function
{//void data type never return value from function
     int c=a-b;
     printf("different between numbers (a-b) is %d\n",c);
}

When the above code is compiled and executed, it produces the following results

different between numbers (a-b) is 10

Program 2

using get input method

#include <stdio.h>
#include <stdlib.h>

int main()
{
    diff();//called the function inside the main
getch();
    return 0;
}
void diff(int a, int b)//argument is passed to this function
{//void never return value from function
    printf("Enter first number for a\n");
    scanf("%d",&a);

    printf("Enter second number for b\n");
    scanf("%d",&b);

    int c=a-b;
    printf("different between (a-b) is %d\n",c);

}

When the above code is compiled and executed, it produces the following results

Enter first number for a
35
Enter second number for  b
15
different between (a-b) is 20

In the above program, diff() function take input from the user find different value and displays result on the screen – argument passed but no return value

Function with return value and without argument

Program 1

#include <stdio.h>
#include <stdlib.h>
int main() {
    printf("answer is:%d",mul());
    getch();
    return 0;
    }
    int mul() {
        int f_no=12;
        int s_no=22;
        int multi;
        multi=f_no*s_no;
        return(multi); }

Program 2

using get input method

#include <stdio.h>
#include <stdlib.h>

int main()
{
    printf("answer is:%d",mul());
    getch();
    return 0;
}
int mul()
{
    int f_no;
    int s_no;
    printf("Enter first number :");
    scanf("%d",&f_no);
    printf("Enter second number :");
    scanf("%d",&s_no);
    int multi;
multi=f_no*s_no;
return(multi);
}

When the above code is compiled and executed, it produces the following results

Enter first number for a :11
Enter second number for  b :22
multiple total is :242

In the above program, mul() function take input from the user find multiple value and displays result on the screen – No argument passed and with the return value

Function with the return and with arguments

Program 1

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int result=divi(50,5);
    printf("Divided value: %d\n",result);
    getch();
    return 0;
}
int divi(int a, int b)
{
    int temp=a/b;
    return temp;
}

When the above code is compiled and executed, it produces the following results

divided value :10

Program 2

using get input method

#include <stdio.h>
#include <stdlib.h>
int main() {
    int result=divi(); //called the function
    printf("answer is:%d",result);
    getch();
    return 0;
    }
    int divi(int num1, int num2)  //argument passed to the function
    {
        printf("Enter first number :");
        scanf("%d",&num1);
        printf("Enter second number :");
        scanf("%d",&num2);
        int temp=num2/num1;
        return temp;
        }

When the above code is compiled and executed, it produces the following results

Enter the first number :9
Enter the second number :45
answer is :5

In the above program, divi() function take input from the user find divided value and displays result on the screen – argument passed and with the return value

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