How to get the first value in a recursive function? - recursion

Question

I'm trying to do a school quiz again. I'm trying to match if my result is equal to number "x". I wrote a recursive function, I always get the value 0, not the one I used to call the function (such as 153). What should I change ?
public static boolean isArmstrong(int x, Armstrong s) {
while (a != true) {
while (x != 0) {
int number = x / 10;
int remain = x % 10;
s.push(remain);
return isArmstrong(number, s);
}
a = true;
}
if (getResult() == x) {
System.out.println("True , result is : " + getResult());
} else {
System.out.println("False , x is : " + x + " result is : " + getResult());
//x always prints out 0 which ends the while loop.But i need to get the x value when i call the function
}
return true;
}
}

Answer 1

You've supplied incomplete information, no definition for the method getResult() nor for the type Armstrong s, but there are still some issues we can address. First, your boolean method isArmstrong() never returns false, only true, so we can't expect it to detect non Armstrong numbers. Second, you're doing too much in your recursive method, both the test for an Armstrong number and the announcing of the result -- these might best be handled by separate methods.
Below's a rework that changes isArmstrong() from a boolean method to one that returns its calculation as an integer. An input value of zero breaks the recursion causing a result to be returned. We use a separate function to compare the argument to isArmstrong() against the returned value to announce success or failure:
public class Armstrong
{
public static int isArmstrong(int x, int power) {
if (x != 0) {
int quotient = x / 10;
int remainder = x % 10;
return (int)Math.pow(remainder, power) + isArmstrong(quotient, power);
}
return 0;
}
public static void main(String args[]) {
int number = 0, power = 0;
if (args.length > 0) {
try {
power = args[0].length();
number = Integer.parseInt(args[0]);
} catch (NumberFormatException e) {
System.err.println("Argument " + args[0] + " must be an integer.");
System.exit(1);
}
}
int result = isArmstrong(number, power);
if (result == number) {
System.out.println("True, result is: " + result);
} else {
System.out.println("False, number is: " + number + " but result is: " + result);
}
}
}
OUTPUT
> java Armstrong 153
True, result is: 153
> java Armstrong 123
False, number is: 123 but result is: 36
> java Armstrong 1634
True, result is: 1634
> java Armstrong 1635
False, number is: 1635 but result is: 2003
>