C# goto Examples

Use the goto statement with labels and in switch cases. Goto transfers control to a new location.

Goto. This keyword transfers control to a named label. It can be used to exit a deeply-nested loop. Goto can help us understand branches and control flow.

Goto notes. The goto statement is fairly powerful. We can use it in a loop or a switch. In practice, many .NET developers never use goto (except maybe in a switch).Switch

An example. This program that uses goto to exit a nested loop. We can use code that does the same thing without goto. But this would require a flag variable (usually a bool) to check.Bool

Part 1: TestGotoNestedLoops contains 3 nested loops. The first loop iterates through numbers [0, 9], as do the two inner loops.

For

Part 2: In this loop, a condition is checked that causes the loop to exit using the goto keyword.

Part 3: With a label, we indicate where a goto-statement should transfer control.

C# program that uses goto, nested loops using System; class Program { static void Main() { Console.WriteLine("RESULT: " + TestGotoNestedLoops()); } static int TestGotoNestedLoops() { // Part 1: 3 nested loops. int dummy = 0; for (int a = 0; a < 10; a++) { for (int y = 0; y < 10; y++) // Run until condition. { // Part 2: use if-statement in loop. // ... Then goto. for (int x = 0; x < 10; x++) // Run until condition. { if (x == 5 && y == 5) { goto Outer; } } dummy++; } // Part 3: the goto label. // ... Control ends up here. Outer: continue; } return dummy; } } Output RESULT: 50

Example, break. We can rewrite code that uses goto to use the break and continue keywords. The goto code uses one fewer variable.

Info: This code uses a flag variable named "ok". It sets "ok" to false and breaks when the exit condition is reached.

True, False

C# program that uses break, for-loop using System; class Program { static void Main() { Console.WriteLine("BREAK: {0}", BreakMethod()); } static int BreakMethod() { int dummy = 0; for (int a = 0; a < 10; a++) { for (int y = 0; y < 10; y++) // Run until condition. { bool ok = true; for (int x = 0; x < 10; x++) // Run until condition. { if (x == 5 && y == 5) { ok = false; break; } } if (!ok) { break; } dummy++; } continue; } return dummy; } } Output BREAK: 50

Switch. Goto can be used in a switch block. Switch allows control to be transferred to another case in this way. This use of goto may be somewhat less confusing than others.

Syntax: There is a special syntax for this construct: it requires goto case or goto default. We examine this syntax form.

GetPrice: GetPrice() performs 3 logical steps, all defined in the switch-statement. We often find switches in single methods like this one.

Note: The method receives the ID of an item. If the ID is equal to 1000, the base price is increased by 10.

And: After this occurs, this ID is treated like a price of 100. It goes to that case.

C# program that uses goto statement in switch using System; class Program { static void Main() { Console.WriteLine(GetPrice(1000)); Console.WriteLine(GetPrice(-1)); Console.WriteLine(GetPrice(int.Parse("100"))); } static int GetPrice(int id) { // // Default price is 5. // int price = 5; // // When id is 1000, add 10 to price before multiplying. // switch (id) { case 1000: price += 10; // <-- Could get from another method goto case 100; case 100: return price * 10; default: return price; } // // 1. // First, if ID is 1000, add ten to default price. // // 2. // If ID is 1000 or 100, multiply price by 10 and return it. // // 3. // If ID is anything else, return price of 5. // } } Output 150 5 50

Error, goto. When we have a goto, a matching label must be present. The label can be at the same scope level, or an enclosing scope (but not in a nested, enclosed scope).

C# program that shows goto error using System; class Program { static void Main() { goto BIRD; Console.WriteLine("BIRD"); } } Output Error CS0159 No such label 'BIRD' within the scope of the goto statement

Warning, goto. If we have a label in a C# program that is not referenced, a warning will appear. This helps us keep our programs free of useless garbage statements.

C# program that shows goto warning using System; class Program { static void Main() { BIRD: Console.WriteLine("BIRD"); } } Output Warning CS0164 This label has not been referenced

Avoid goto. In my experience, it is best not to use goto, even in switch statements. Using a method to encapsulate logic is better—it is more versatile, and can promote code sharing better.

Benefits, switch. Quality code is structured into discrete methods. We can call the same method with different values from a switch.

But: In certain cases we may benefit from goto in switch when trying to reduce method size. A benchmark shows this effect.

Method Size Test

Info: The greatest benefit of switches on ints or non-string constants here is that the low-level MSIL jump statement is used.

Int, uint Switch Enum IL: switch

Research. Goto was part of the 1960s emergence of structural programming. In "Go To Statement Considered Harmful," Dijkstra observed how goto-statements make logic harder to follow.

And: New options, like methods, are clearer. With them, programs are less likely to deteriorate into unfathomable messes.

Quote: The go to statement as it stands is just too primitive, it is too much an invitation to make a mess of one's program (Edsger W. Dijkstra).

Quote: Formally, the goto is never necessary, and in practice it is almost always easy to write code without it.... It does seem that goto statements should be used rarely, if at all (The C Programming Language).

A summary. Goto is part of the C# language. But usually it is not needed, and often teams will prefer to not allow it in programs. Consider polymorphism instead of goto.Inheritance

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C# goto Examples

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