Why no variable to store method return value (Delegates and Methods)

Question

public int CalculateProduct(int num1, int num2) Requires a return type of int. However, in main, when CalculateProduct is called, no variable is assigned to accept the int being returned. I don't understand why. Thanks!

using System;
delegate void NotifyCalculation(int x, int y, int result);
class Calculator {
    NotifyCalculation calcListener;
    public Calculator(NotifyCalculation listener) {
        calcListener = listener;
    }
    // THIS IS NOT A VOID. IT HAS A RETURN TYPE OF INT
    public int CalculateProduct(int num1, int num2) {
        // perform the calculation
        int result = num1 * num2;
        // notify the delegate that we have performed a calc
        calcListener(num1, num2, result);
        // return the result
        return result;
    }
}
class CalculationListener {
    public static void CalculationPrinter(int x, int y, int result) {
        Console.WriteLine("Calculation Notification: {0} x {1} = {2}", 
            x, y, result);
    }
}
class Listing_04 {
    static void Main(string[] args) {
        // create a new Calculator, passing in the printer method
        Calculator calc = new Calculator(CalculationListener.CalculationPrinter);
        // THE RETURN TYPE IS NOT BEING CAPTUREED HERE WHY?
        calc.CalculateProduct(10, 20);
        calc.CalculateProduct(2, 3);
        calc.CalculateProduct(20, 1);
        // wait for input before exiting
        Console.WriteLine("Press enter to finish");
        Console.ReadLine();
    }
}

Answer 1

Your code works fine - if you're asking why CalculateProduct must be declared as:

public int CalculateProduct(int num1, int num2) 

This is because you're returning the result:  "return result;"

If you want to declare it as void, you can - just don't return anything:

   public void CalculateProduct(int num1, int num2)
    {
        // perform the calculation
        int result = num1 * num2;
        // notify the delegate that we have performed a calc
        calcListener(num1, num2, result);
        // Don't return the result
        // return result;
    }

This will give the same results as your original code (since you never used the return value).

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Reed Copsey, Jr. - http://reedcopsey.com
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Answer 2

Hi Jacob;

Just because a function returns a value does not require you to capture it in a variable, by not capturing the value it is thrown away.

You state, "public int CalculateProduct(int num1, int num2) Requires a return type of int", only because the function signature defines one. In this case you can remove the int return type in the signature and comment out the return statement and all will still work.

  

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Fernando (MCSD)

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Answer 3

thanks guys! Very much appreciated. I'm from a VB6 background and from what i can remember, functions in VB6 required that the return value be captured.

Thanks for answering my question.

Answer 4

thanks guys! Very much appreciated. I'm from a VB6 background and from what i can remember, functions in VB6 required that the return value be captured.

You need to capture the result if you use the function call syntax.

Function F(i As Integer)

can be called

x = F(42) 'capturing the result

or

F 42 'not capturing the result

A function without parameters can be called

x = F 'capturing the result

or

F 'not capturing the result

Answer 5

 

Not a problem, Glad I was able to help.

  

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Fernando (MCSD)

If a post answers your question, please click "Mark As Answer" on that post and "Mark as Helpful".