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The Difference Between Printing and Returning

1:42 with Jay McGavren

It's important to know that having a method print output using Console.WriteLine is not the same as having a method return a value.

It's important to know that having a method print output using Console.WriteLine is not the same as having a method return a value. If you confuse the two, your programs are going to behave strangely, and you won't know why. So I wanted to spend this video clarifying the difference.

  • Here's a version of our program with the Subtract method removed.
  • Suppose I remove the return statement from the Add method, and instead passed the result of adding the numbers to Console.Writeline: Console.WriteLine(first + second);
  • I'll get an error: "'Program.Add(double, double)': not all code paths return a value"
    static double Add(double first, double second)
    {
        Console.WriteLine(first + second);
    }
  • Converting the return type of Add to void gets the Add method declaration to compile...
    • But then we get the error "Cannot implicitly convert type 'void' to 'double'" when the code down in Main expects a return value.
    static void Add(double first, double second)
    {
        Console.WriteLine(first + second);
    }
    static void Main(string[] args)
    {
        double total = Add(3, 5);
        Console.WriteLine(total);
    }
  • Just remember, if you want your method to give information to a human, you can call Console.WriteLine.
  • But if you want your method to give information back to your program, you need to specify a return type and use the return keyword instead.
    static double Add(double first, double second)
    {
        return first + second;
    }
  • 0:00

    It's important to know that having a method print output using console dot

  • 0:04

    WightLine is not the same as having a method return a value.

  • 0:08

    If you confuse the two, your programs are going to behave strangely, and

  • 0:11

    you won't know why.

  • 0:12

    So I wanted to spend this video clarifying the difference.

  • 0:16

    Here's a version of our earlier program with the subtract method removed.

  • 0:20

    Suppose I remove the return statement from our add method, and

  • 0:23

    instead pass the result of adding the numbers to console dot WriteLine?

  • 0:28

    If I save this and attempt to run it, I'll get an error.

  • 0:32

    This is on line five, which is right here.

  • 0:36

    And it says not all code paths return a value.

  • 0:39

    I can get the add method to compile by changing its return type to void,

  • 0:44

    since it doesn't actually return a value now.

  • 0:48

    But if I save this and try running that, dot net run,

  • 0:52

    I get an error down on line 12.

  • 0:54

    It says cannot implicitly convert type void to double.

  • 1:01

    The code down here in Main expects a return value so

  • 1:04

    that it can assign it to this variable.

  • 1:08

    But the add method is no longer providing one.

  • 1:11

    So just remember, if you want your method to give information to a human,

  • 1:14

    you can call Console dot WriteLine.

  • 1:17

    But if you want your method to give information back to your program,

  • 1:20

    you need to specify a return type.

  • 1:22

    So let’s change this return type back to double from void.

  • 1:30

    And you need to use the return keyword return first plus second.

  • 1:35

    Let me save this and try running it.

  • 1:40

    And now, it's working again.

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