C Program to Find Factorial of a Positive Negative and 0 Number

C Program to Find Factorial of a Any Number

The factorial of a any 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 n is given by:

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

 And, the factorial of 0 is 1, 0! = 1

Example: Factorial of a Number

#include<stdio.h>
#include<conio.h>
int main()
{
int a;
int fact=1;
printf("Enter an integer: \n");
scanf("%d", &a);
if(a<0)
{
a=-a;
for(int i=1; i<=a; i++)
{
fact=fact*i;
}
printf("Factorial of the %d=%d", -a, -fact);
return -fact;
}
else
{
if(a>0)
{
for(int i=1; i<=a; i++)
{
fact=fact*i;
}
printf("Factorial of the %d = %d", a, fact);
return fact;
}
else
{
if(a==0)
{
printf("The factorial of %d = 1", a);
}
}
}
getch();
}

Output 1:

Enter an integer: 10
Factorial of 10 = 3628800

Output 2:

Enter an integer: -10
Factorial of 10 = -3628800

Output 3:

Enter an integer: 0
Factorial of 0 = 1

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.

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