.NET 1.1

C# Goto Statement

The thirty-third part of the C# Fundamentals tutorial reviews the use of the jump statement, 'goto'. This command is rarely used and often scorned but does provide a valuable function when used with the switch statement to control program flow.

Spaghetti Code

The goto statement is a simple command that unconditionally transfers the control of the program to another statement elsewhere in the code. The command is criticised often with some people advocating its removal from all high-level programming languages because it can lead to spaghetti code. This occurs when there are so many goto statements or similar jump statements that the code becomes difficult to read and maintain. However, there are many programmers who point out that the goto statement, when used carefully, provides an elegant solution to some problems.

Basic Syntax

The basic syntax of the goto statement is very simple. Firstly a label must be created at some point in the code. This label is the destination for the jump. A label is defined by simply providing a name for the label followed by a colon symbol (:). The goto statement references the label as shown in the following example code:

Console.WriteLine("This will get outputted.");

goto myLabel;

Console.WriteLine("This will not get outputted.");

myLabel:

Console.WriteLine("This will not get outputted.");

It should be noted that the destination label must be in the same method as the goto that calls it. In some cases, the label must be within the same code block or code structure, as with the use of goto within a switch statement, explained below.

Goto and Switch

When using the switch code structure for multi-way conditional processing, each case statement also defines a label. This means that the goto command may be used to jump between the various cases, allowing a cascading chain of case statements to be executed rather than just a single item. When using gotos in this manner, a break statement is not required in a case that ends with a goto.

The following example shows a switch statement used to interpret a status code. In the example, the "Warn" case is executed first, followed by the "Complete" case. Even this small example shows how quickly code can become difficult to read if the goto command is used carelessly.

string statusCode = "Warn";

switch (statusCode)
{
    case "Warn":
        Console.WriteLine("Completed with warnings.");
        goto case "Complete";
    case "Err":
        Console.WriteLine("Completed with errors.");
        goto case "Complete";
    case "Complete":
        Console.WriteLine("Completed.");
        break;
    case "Fail":
        Console.WriteLine("Failed to complete.");
        break;
    default:
        Console.WriteLine("Unknown status code");
        goto case "Fail";

NB: The goto command may only be used to jump between cases including the default case. Jumps into or out of the entire switch statement are not permitted.