Java factorial with loop

[Atlanta15Braves]

I need a program that will return an integers factorial, but only when the number entered is between 0 and 20. I have the code to disregard anything below 0 and above 20, but something with my math and/or syntax is off and I dont fully comprehend how to fix the error. My code is below....

import java.util.Scanner;

public class Factorial {

    public static void main(String[] args) {
        int num; // number to find factorial of
        long fac; // factorial so far
        Scanner scan = new Scanner(System.in);

        // Get value to compute factorial of
        System.out.print("Please enter a non-negative integer: ");
        num = scan.nextInt();

        // Compute and print factorial
        // your code here...
        while(num < 0 || num > 20){
            System.out.println("Factorial is undefined for negative or large numbers");
            System.out.print("Please enter an integer number between 0 and 20: ");
            num = scan.nextInt();
        }
//        while(num > 0 || num < 20) {
//            for (int i = 1; i < 50; i ++){
//            fac = num(i) * num(i -1);
//            }
for (int i = 1 ; i <= 20; i++){
num=num - 1 * i;
}
System.out.println("The factorial is: " + num);

    }
  }
}

[zeroliken]

in your loop at line 25 you dont need to iterate it 20 times but you use the input instead, use another variable to store the factorial

[Atlanta15Braves]

So you are saying where I have I <= 20, I should have my user input as "num <= 20" and use the variable fac as my factorial variable?

[piyush09]

you need to update the code at line25,26,27,28 as

if(num ==0)
{
 fac = 1;
}
else{
 for(int i=1;i<=num;i++){
  fac = fac*num
 }
}
System.out.println("The factorial is: " + fac);

``

[JamesCherrill]

@piyush
Please don't just spoon feed raw code to people. All that teaches them is how easy it is to cheat with a quick copy/paste. You didn't even attempt to explain why you made the changes you did. Give people assistance that helps them learn how to fix problems for themselves.