#include <stdio.h>

int main(void)
{
    int num = 0;
    char yn = 'y';
    int i = 1;
    int fac = 1;
    //defining all the vars
    while('y' == yn)
    {
        do{
            printf("Please enter a positive number: ");
            scanf("%d",&num);
            getchar();
            if(num<0)
            {
                printf("Invalid input!\n");
            }
            //getting a number from user
        }while (num<0);
        //loop will run once to get input from user , and keep running if number is invalid until user enters a valid number(positive number)
        if (0 == num)
        {
            printf("The factorial of 0 is 1");
        }
        //The factorial of 0 is 1
        else
        {
            for(i=1 ; i<num+1 ; i++)
            {
                fac *= i;
            }
            //calculates the factorial number of the number the user entered
            printf("The factorial of %d is %d\n",num , fac);
        }
        //printing the factorial number of the number the user entered
        printf("Would you like to try again?\n");
        printf("Click 'y' for yes or other key for no: ");
        scanf("%c", &yn);
        getchar();
        //asking the user if he wants to try again, getting input from user
        fac=1;
        //resetting vars
    }
    return 0;
}