C Program to Find Factorial of a Number Using Function

Howdy readers, today you will learn how to write a program to find the factorial of a number using a function in the C Programming language.

The below program prompts the user to enter a positive integer, then it computes its factorial using a user-defined function and for loop.

So, without any delay, let’s begin this tutorial.

C Program to Find Factorial of a Number Using Function

C Program

// C Program to Find Factorial of a Number Using Function 
#include <stdio.h>
int fact(int );

int main(){
    int num, factorial;
    
    // Asking for input
    printf("Enter a positive integer: ");
    scanf("%d", &num);
    
    // Calling out function 
    factorial = fact(num);
    
    // Displaying result
    printf("The factorial of %d is: %d", num, factorial);
    
    return 0;
}

int fact(int n){
    int i, f = 1;
    for (i = 1; i <= n; i++){
        f = f * i;
    }
    return f;
}

Output

Enter a positive integer: 7
The factorial of 7 is: 5040

Explanation

    int num, factorial;

We have declared two int data type variables named num and factorial.

    // Asking for input
    printf("Enter a positive integer: ");
    scanf("%d", &num);

The user is asked to enter a positive integer. This value gets stored in the num named variable.

    // Calling out function 
    factorial = fact(num);

Then, the user-defined function named fact is called in the main function.

int fact(int n){
    int i, f = 1;
    for (i = 1; i <= n; i++){
        f = f * i;
    }
    return f;
}

We have defined a function named fact() which computes the factorial of a number using for loop statement.

Suppose the user enters a number 3, then:

• 1st For Loop Iteration: (i = 1; i <= 3; i++), here the condition is True.
• f = f * i = 1 * 1 = 1

• 2nd For Loop Iteration: (i = 2; i <= 3; i++), the condition is True.
• f = f * i = 1 * 2 = 2

• 3rd For Loop Iteration: (i = 3; i <= 3; i++), the condition is True.
• f = f * i = 2 * 3 = 6

• 4th For Loop Iteration: (i = 4; i <= 4; i++), the condition is False, so the program terminates and returns f whose value is 6 for this case.

    // Displaying result
    printf("The factorial of %d is: %d", num, factorial);

The called out value which gets stored in the factorial named variable is displayed on the screen using printf() function.

Output

Enter a positive integer; 7
The factorial of 7 is: 5040

Conclusion

I hope after reading the program and the explanation part, you understand how to write a program to find the factorial of a number using a function in C Programming language.

If you have any queries regarding the program, then let us know in the comment section. We will be pleased to solve all of your queries.