C program to calculate the factorial of a number

Comprehensive Collection of C Programming Examples

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

To understand this example, you should understand the followingC programmingTopic:

• C data types

• C programming operators

• C if ... else statement

• C for loop

The factorial of positive number n is:

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

Factorial of negative numbers does not exist. The factorial of 0 is1.

Calculate the factorial of a number

#include <stdio.h>
int main() {
　　　　int n, i;
　　　　unsigned long long fact =　1;
　　　　printf("Enter an integer: ");
　　　　scanf("%d", &n);
　　　　//If the user enters a negative integer, display an error
　　　　if (n < 0)
　　　　　　　　printf("Error! Factorial of negative numbers does not exist.");
　　　　else {
　　　　　　　　for (i =　1; i <= n;　++i) {
　　　　　　　　　　　　fact　*= i;
　　　　　　　　}
　　　　　　　　printf("%d's factorial = %llu", n, fact);
　　　　}
　　　　return 0;
}

Output result

Enter an integer:　10
10　factorial ==　3628800

The program takes a positive integer from the user and calculates the factorial using a for loop.

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

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

You can alsoUse recursionFind the factorial of a number.

Comprehensive Collection of C Programming Examples