对 C# 中的返回方法和空白感到困惑

Question

Want feedback if i`m correct here?

Use void if you are not returning anything in a method, otherwise

1. Name your data types used in the method criteria before method name.
2. use Return in the method before the calculation or output.

So something like this.

    static int MyMethod(int x) 
{
  return 5 + x;
}

static void Main(string[] args)
{
  Console.WriteLine(MyMethod(3));
}

// Outputs 8 (5 + 3)

What if my method has ints and doubles? Do I write as follows? (another words do I have to mention every type i`m using prior to the method name?

static int double myMethod (int x, double y) 

Even with that I dont know when is a method void? It seems my methods all return values. Isnt the following returning the values of the arguments? So why should I label it void?

static void MyMethod(string fname, int age) 
{
  Console.WriteLine(fname + " is " + age);
}

static void Main(string[] args)
{
  MyMethod("Liam", 20);
  MyMethod("Jenny", 25);
  MyMethod("Tom", 31);
}

I can only think that a void means there is no new calculation being done in the actual method body, passing arguments into a method and spitting them out for user viewing does not mean its "returning a value", I dont know what i`m talking about.

Answer 1

Let's be completely clear about what these bullets mean.

Use void if you are not returning anything in a method, otherwise

In this context, "return" means that the method provides an output that can be assigned to a variable by the caller. For example

int Return10()
{
    return 10;
}

...allows the caller to do this:

int x = Return10();
Console.WriteLine(x);  //Outputs "10"

A method should "return" void when its results cannot be assigned. For example, if the results are printed on the screen.

void Print10()
{
    Console.WriteLine("10"); //Prints 10 to the screen
}

...which allows the caller to do this:

Print10();

You cannot assign it because it doesn't return anything. This doesn't work:

int x = Print10(); //Compiler error

Name your data types used in the method criteria before method name.

A method can return exactly one value or object. So "types" here is wrong. You can only specify one type.

Use return in the method before the calculation or output.

This is a little misleading. The return keyword should be followed by an expression which can be assigned.

int Return10()
{
    return 10 + 10; //Is okay because it's an expression and could be assigned
}

int Return10()
{
    var x = 10 + 10; 
    return x; //This is also okay; in fact it does exactly the same thing as the previous example
}

int Return10()
{
    return Console.WriteLine("10"); //Compiler error; can't be assigned to anything.
}

By the way, a method can also output something and return it:

int WriteAndReturn10()
{
    int x = 10;
    Console.WriteLine(x); 
    return x;
}

Answer 2

I am going to address the following

What if my method has ints and doubles? Do I write as follows? (another words do I have to mention every type i`m using prior to the method name?

There are no built in ways or syntax to return more than one type from a method as the return parameter.. This is basically historical and has been this way since dinosaurs roamed the earth.

However, there are lots of options that achieve the same result. For instance, you could use a custom struct, you could use out parameters , you could use a class, or a delegate parameter of some kind. However, a modern succinct approach might be to use a Value Tuple :

static (int someInt, double someDouble) myMethod (int x, double y) 
{
    return (x,y);
}

_{Fun Fact : even though this looks like you a returning more than one type, you are actually just invoking a special syntax that wraps your return parameters in a single type of struct}

Usage

var result = myMethod(1,2.2);
Console.WriteLine(result.someInt);
Console.WriteLine(result.someDouble);

Or if you want to get fancy, you can use the newer deconstructed syntax

var (someInt, someDouble) = myMethod(1,2.2);
Console.WriteLine(someInt);
Console.WriteLine(someDouble);

---

Additional Resources

• return (C# Reference )

• Methods (C# Programming Guide)

• Tuple types (C# reference)

• out parameter modifier (C# Reference)

• ref (C# Reference)

• Using Delegates (C# Programming Guide)