C Example for Beginners: C Program to Find Factorial of a Number

(C programming Example for Beginners)

C Program to Find Factorial of a Number

In this example, you will learn to calculate the factorial of a number entered by the user.

The factorial of a positive number n is given by:

factorial of n (n!)= 1 * 2 * 3 * 4....n

The factorial of a negative number doesn’t exist. And, the factorial of 0 is 1.

Factorial of a Number

#include <stdio.h>
int main(){
    int n, i;
    unsigned long long fact = 1;
    printf("Enter an integer: ");
    scanf("%d", &n);

    // shows error if the user enters a negative integer
    if (n < 0)
        printf("Error! Factorial of a negative number doesn't exist.");
    else {
        for (i = 1; i <= n; ++i) {
            fact *= i;
        printf("Factorial of %d = %llu", n, fact);

    return 0;


Enter an integer: 10
Factorial of 10 = 3628800

This program takes a positive integer from the user and computes the factorial using for loop.

Since the factorial of a number may be very large, the type of factorial variable is declared as unsigned long long.

If the user enters a negative number, the program displays a custom error message.



C Example for Beginners: C Program to Find Factorial of a Number

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