How to Exit a Method without Exiting the Program?

I am still pretty new to C# and am having a difficult time getting used to it compared to C/CPP.

How do you exit a function on C# without exiting the program like this function would?

if (textBox1.Text == "" || textBox1.Text == String.Empty |开发者_开发知识库| textBox1.TextLength == 0)
    textBox3.Text += "[-] Listbox is Empty!!!!\r\n";
System.Environment.Exit(0);

This will not allow return types and if left alone it will keep going on through the function unstopped. Which is undesirable.

There are two ways to exit a method early (without quitting the program):

• Use the return keyword.
• Throw an exception.

Exceptions should only be used for exceptional circumstances - when the method cannot continue and it cannot return a reasonable value that would make sense to the caller. Usually though you should just return when you are done.

If your method returns void then you can write return without a value:

return;

Specifically about your code:

• There is no need to write the same test three times. All those conditions are equivalent.

• You should also use curly braces when you write an if statement so that it is clear which statements are inside the body of the if statement:

  if (textBox1.Text == String.Empty)
  {
      textBox3.Text += "[-] Listbox is Empty!!!!\r\n";
  }
  return; // Are you sure you want the return to be here??
  

• If you are using .NET 4 there is a useful method that depending on your requirements you might want to consider using here: String.IsNullOrWhitespace.

• You might want to use Environment.Newline instead of "\r\n".
• You might want to consider another way to display invalid input other than writing messages to a text box.

In addition to Mark's answer, you also need to be aware of scope, which (as in C/C++) is specified using braces. So:

if (textBox1.Text == "" || textBox1.Text == String.Empty || textBox1.TextLength == 0)
    textBox3.Text += "[-] Listbox is Empty!!!!\r\n";
return;

will always return at that point. However:

if (textBox1.Text == "" || textBox1.Text == String.Empty || textBox1.TextLength == 0)
{
    textBox3.Text += "[-] Listbox is Empty!!!!\r\n";
    return;
}

will only return if it goes into that if statement.

I would use return null; to indicate that there is no data to be returned

The basic problem here is that you are mistaking System.Environment.Exit for return.

@John, Earlz and Nathan. The way I learned it at uni is: functions return values, methods don't. In some languages the syntax is/was actually different. Example (no specific language):

Method SetY(int y) ...
Function CalculateY(int x) As Integer ...

Most languages now use the same syntax for both versions, using void as a return type to say there actually isn't a return type. I assume it's because the syntax is more consistent and easier to change from method to function, and vice versa.

If the function is a void, ending the function will return. Otherwise, you need to do an explicit return someValue. As Mark mentioned, you can also throw an exception.