How do I return a value from a Java function?

Question

I am trying to get the following program to work:

public class funWithNumbers {
public static void main (String[] args) {
    int ten = 10;
    int subend = 7;
    int result = ten - subend;
    int success = 0;
    int trials = 750;
    for (int i=0; i<trials; i++) {
        double randomNumber = Math.random();
        randomNumber = randomNumber * 200;
        randomNumber++;
        int randNum = (int) randomNumber;
        int mystery = randNum;
        returnTen(mystery, subend, result, success);
    }
    int accuracy = (success / trials) * 100;
    System.out.println("Trials Run: " + trials);
    System.out.println("We can say that the number " + result + " indeed equals " + result + " with " + accuracy + "% accuracy.");
}
public static int returnTen(int mystery, int subend, int result, int success) {
    int original = mystery;
    mystery = mystery + mystery;
    mystery = mystery * 5;
    mystery = mystery / original;
    mystery = mystery - subend;
    if (mystery == result) {
        success++;
    }
    return success;
}
}

Everything in this program works except that last statement (return success). For whatever reason, I cannot return the value from the returnTen function back to the main program. I tried debugging the program using System.out.println() statements along the way (not included above) and within the returnTen function itself, the success variable is successfully incremented. But I cannot get that to pass back to the main function.

What should happen: You'll notice the function is basically a common number trick. The end result of mystery should be 3 (which is what result is). Therefore, success should always be incremented every time the function runs. Which means that accuracy should be 100%, and the statement printed out should read We can say that the number 3 indeed equals 3 with 100% accuracy

What is happening: The end statement currently prints We can say that the number 3 indeed equals 3 with 0% accuracy which is obviously not true - success is not being passed back and therefore, accuracy is being calculated as 0%.

EDIT: Changing returnTen(mystery, subend, result, success); to success = returnTen(mystery, subend, result, success); changes the end statement from 0% to 25000%. UPDATE: Fixed the problem - success = needed to be added and I had to change success / result to success / trials - oops!

Possible duplicate of Is Java "pass-by-reference" or "pass-by-value"? — SomeJavaGuy
– SomeJavaGuy, Commented Dec 28, 2016 at 14:41
Pretty much this question could be the dupe, i fell like you are using it as it would pass a reference to the int's, in this case success, but you need to store it somewhere as success = returnTen(...) — SomeJavaGuy
– SomeJavaGuy, Commented Dec 28, 2016 at 14:42
Your edit should probably be a new question, since it likely identifies a symptom from a different problem. — Warren Dew
– Warren Dew, Commented Dec 28, 2016 at 14:48
I agree with Kevin, returnTen(mystery, subend, result, success); this call clearly forget to store the return value so this expect that the success pass will be change after the call. — AxelH
– AxelH, Commented Dec 28, 2016 at 14:49
And before creating a new question, since this is totaly different, this probably need to be investigate a bit from your part ;) — AxelH
– AxelH, Commented Dec 28, 2016 at 14:50

Warren Dew · Accepted Answer · 2016-12-28 14:44:32Z

3

Your returnTen() function is returning the value, but your code is not using that value. To use the return value, the line:

returnTen(mystery, subend, result, success);

should be:

success = returnTen(mystery, subend, result, success);

answered Dec 28, 2016 at 14:44

Warren Dew

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T.J. Crowder · Accepted Answer · 2016-12-28 14:44:43Z

3

The problem isn't that return success; isn't working (it is), it's that you're not using the return value. When you call the function, you need to use the return value:

    success = returnTen(mystery, subend, result, success);
//  ^^^^^^^^^^

answered Dec 28, 2016 at 14:44

T.J. Crowder

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Coop · Accepted Answer · 2016-12-28 14:50:06Z

0

In order to make use of a return a value from a function you must assign it to a variable or use it as a test condition, etc.

if(returnTen(mystery, subend, result, success) > 0){
    System.out.println("returnTen returned an int value");
}

Currently your code is discarding the return value since it is not assigned to anything.

answered Dec 28, 2016 at 14:50

Coop

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