**What is factorial of a number?**

- Factorial is denoted by the symbol ‘!’. For example, factorial of a number 4 is denoted as 4!. Factorial of a number is defined as the product of “the number and all integers less than that number except zero and negative integers”.
- Natural numbers ( non-negative integers ) which are greater than zero are used for factorial concept.

**Factorial Example:**

Zero factorial (0!) = 1

one factorial (1!) = 1

Two factorial (2!) = 2*1 = 2

Three factorial (3!) = 3*2*1 = 6

Four factorial (4!) = 4*3*2*1 = 24

Five factorial (5!) = 5*4*3*2*1 = 120

etc…

The common mathematical formula for finding factorial of the number ‘n’ is given below.

n! = n ( n – 1)( n – 2)( n – 3) …… (1)

#include <stdio.h> int main() { int i,fact=1,num; printf("\nPlease enter a number to find factorial : "); scanf("%d",&num); if (num<0) { printf("\nPlease enter a positive number to"); printf(" find factorial and try again. \n"); printf("\nFactorial can't be found for negative"); printf(" values. It can be only positive or 0 \n"); return 1; } for(i=1;i<=num;i++) fact=fact*i; printf("\n"); printf("Entered number is %d and it's factorial (%d!) is %d\n",num,num,fact); return 0; }

**OUTPUT**

Please enter a number to find factorial : 7 Entered number is 7 and it’s factorial (7!) is 5040