In mathematics, the factorial of a positive integer number n is denoted by n!, and it is the product of all positive integers from 1 to less than or equal to n. Note that factorial of number 0 is 1 & factorial of a negative number doesn’t exist.

For example, factorial of number 5 is product of numbers from 1 to 5 as 1*2*3*4*5 which is 120.

## The factorial of a positive number n is given by:

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

## C Program – Loops Example – To Find Factorial of Number

#include <stdio.h> int main() { int n, i; long fact = 1; printf("\n\t----------------------------------------------------------------\n"); printf("\n\tEnter Number : "); scanf("%d",&n); // if the user enters a negative integer , show message if (n < 0) { printf("\n\t Factorial of a negative number doesn't exist."); } else { for(i=1; i<=n; i++) { fact = fact * i; } printf("\n\tFactorial of %d = %ld", n, fact); } printf("\n\t-----------------------------------------------digitalpadm.com\n"); return 0; }

In this program, variable n is to input number if it is less than zero , means it is negative hence show message as “factorial of negative number does not exists”.

if number n is positive , then find factorial by finding the product of numbers from 1 to n. here for loop is used for iteration. initially value of fact variable is 1.

for,

1st iteration i=1 & value of fact is 1 , so new value of fact variable is fact=1*1 , which is **1**

2nd iteration i=2 & value of fact is 1 , so new value of fact variable is fact=1*2 , which is **2**

3rd iteration i=3 & value of fact is 2 , so new value of fact variable is fact=2*3 , which is **6**

4th iteration i=4 & value of fact is 6 , so new value of fact variable is fact=6*4 , which is **24**

5th iteration i=5 & value of fact is 24 , so new value of fact variable is fact=24*5 , which is **120**

Download code : c-program-factorial-program-step-by-step-explain.c (108 downloads)

Output of program

C Program – Loops Example – Fibonacci Series up to N terms