#include <stdio.h>


int main()
{

    char keepRunning = 'y';
    //declaring var

    do{

            int i  = 0;
            int factorial = 1;
            int number = 0;
            //declaring vars so that every time that the functions runs, their value will be the above value

            printf("Enter a valid number: ");
            scanf("%d", &number);
            getchar();
            //getting an input from the user

            while(0 > number){
                printf("Enter a valid number: ");
                scanf("%d", &number);
                getchar();
            }
            //if the number is not valid, ask the user to put the number again
            if(0 == number){
                factorial = 1;
            }
            //0! = 1
            else{
                for(i = 1; i < number + 1; i++){
                    factorial = factorial * i;
                }
            }
            //from 1 to the number, it multiplies all of number the numbers.
            printf("factorial of %d is %d \n", number, factorial);
            //prints the factorial
            printf("Would you like to try again?\nClick 'y' for yes or other key for no: ");
            scanf("%c", &keepRunning);
            getchar();
            //asks the user if he wants to try again, "type 'y' if you do"

            factorial = 1;


    }while(keepRunning == 'y');

    return 0;

}