C Language program to calculate factorial of a number

Introduction: In this article i will explain how to create  a program to find/get/calculate factorial of entered number using For loop in C language.

Factorial:   Mathematically, the formula for the factorial is as follows. If n is an integer greater than or equal to 1, then

n ! = n ( n - 1)( n - 2)( n - 3) ... (3)(2)(1)

Rule: n! = n*(n-1)!

   So 1! = 1

        2! = 2×1 = 2

        3! = 3×2×1 = 6

        4! = 4×3×2×1 = 24

        5! = 5×4×3×2×1 = 120

        6!=  6×5×4×3×2×1 = 720

 or we can say if n=6 then factorial of 6 will be calculated as 1*2*3*4*5*6= 720 or 6*5*4*3*2*1=720.  So 6 != 720.

Implementation: Let's create a program to calculate Factorial of a number.

 #include<conio.h>

#include<stdio.h>

int main()

{
  unsigned long long int fact=1; 

  int i,n;

  clrscr();

  printf("Enter any positive number to calculate its factorial: ");

  scanf("%d",&n);

  for(i=1;i<=n;i++)

  {

    fact=fact*i;

  }

   printf("\nFactorial of %d = %llu",n,fact);

   getch();

   return 0;

}

Note:  We can also use 

  for(i=n;i>=1;i--)

  {

    fact=fact*i;

  }

instead of 

  for(i=1;i<=n;i++)

  {

    fact=fact*i;

  }

Now Run the program using Ctrl+F9