goto ExamplesUse the goto statement with labels and in switch cases. Goto transfers control to a new location.
This page was last reviewed on Apr 26, 2023.
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.
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).
This program 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.
Part 1 TestGotoNestedLoops contains 3 nested loops. The first loop iterates through numbers [0, 9], as do the two inner loops.
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.
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; } }
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
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; } }
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.
Here 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.
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. // } }
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).
using System; class Program { static void Main() { goto BIRD; Console.WriteLine("BIRD"); } }
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.
using System; class Program { static void Main() { BIRD: Console.WriteLine("BIRD"); } }
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.
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
Intermediate 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.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Apr 26, 2023 (edit).
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