C Program to Find Factorial of a Number | | c programming examples | c programming examples for practice

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

To understand this example, you should have the knowledge of the following C programming topics:

C Data Types

C Programming Operators

C if...else Statement

C for Loop

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;

}

Output

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.

You can also find the factorial of a number using recursion.

 

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