The factorial of a positive integer n is equal to 1*2*3*...n. You will learn to calculate the factorial of a number using for loop in this example.
The factorial of a positive number n is given by:
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,
0! = 1
Example: Factorial of a Number
int n, i;
unsigned long long factorial = 1;
printf("Enter an integer: ");
// show error if the user enters a negative integer
if (n < 0)
printf("Error! Factorial of a negative number doesn't exist.");
for(i=1; i<=n; ++i)
factorial *= i; // factorial = factorial*i;
printf("Factorial of %d = %llu", n, factorial);
Enter an integer: 10
Factorial of 10 = 3628800
This program takes a positive integer from the user and computes factorial using for loop.
Since the factorial of a number may be very large, the type of factorial variable is declared as
unsigned long long.
If the user enters negative number, the program displays error message.