C Program to Find Factorial of a Number

The factorial of a positive number n is given by:

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

The factorial of a negative number doesn’t exist. And, the factorial of 0 is 1.

Factorial of a Number

1.   #include <stdio.h>
2.   int main() {
3.   int n, i;
4.   unsigned long long fact = 1;
5.   printf("Enter an integer: ");
6.   scanf("%d", &n);
8.   // shows error if the user enters a negative integer
9.   if (n < 0)
10.   printf("Error! Factorial of a negative number doesn't exist.");
11.   else {
12.   for (i = 1; i <= n; ++i) {
13.   fact *= i;
14.   }
15.   printf("Factorial of %d = %llu", n, fact);
16.   }
18.   return 0;
19.   }

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