C Program to Print Factorial of a Number

Write a Program to Calculate the Factorial of a Number in C.

Definition of a Factorial:

The factorial of a number is the multiplication of all the numbers between 1 and the number itself. It is written like this: n!. So the factorial of 2 is 2! (= 1 × 2).

To Calculate a Factorial:

1. 0! = 1
2. n! = (n - 1)! × n

The factorial of 0 has value of 1, and the factorial of a number n is equal to the multiplication between the number n and the factorial of n-1.

Code:

/*Program to print given number of factorial*/
#include <stdio.h>
int main()
{
    int num;
    // Taking Input from the user
    printf("Enter a number: ");
    scanf("%d", &num);
    int product = 1;
    // Checking for negative input
    if (num < 0)
    {
        printf("Factorial of a negative number is not defined.\n");
    }
    else
    {
        // Calculate the number of factorial
        for (int i = 1; i <= num; i++)
        {
            product = product * i;
            //  Output result
            printf("The factorial of %d is :%d\n", i, product);
        }
    }
    return 0;
}
  

Explanation:

1. First of all, the user enters a number.
2. If the number is negative, the program displays an error message, since factorials are only defined for positive integers.
3. If the number is positive, a for loop calculates the factorial by multiplying numbers from 1 to num.

Output:

    Enter a number: 5
    
    The factorial of 1 is :1
    The factorial of 2 is :2
    The factorial of 3 is :6
    The factorial of 4 is :24
    The factorial of 5 is :120