# switch statement

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Executes code according to the value of an integral argument.

Used where one or several out of many branches of code need to be executed according to an integral value.

### Syntax

`switch (` expression `)` statement |  |

expression | - | any expression of integer type (char, signed or unsigned integer, or enumeration)
statement | - | any statement (typically a compound statement). `case:` and `default:` labels are permitted in statement, and break; statement has special meaning.

`case` constant_expression `:` statement | (1) |
`default` `:` statement | (2) |

constant_expression | - | any integer constant expression

### Explanation

The body of a switch statement may have an arbitrary number of `case:` labels, as long as the values of all constant_expressions are unique (after conversion to the promoted type of expression). At most one `default:` label may be present (although nested switch statements may use their own `default:` labels or have `case:` labels whose constants are identical to the ones used in the enclosing switch).

If expression evaluates to the value that is equal to the value of one of constant_expressions after conversion to the promoted type of expression, then control is transferred to the statement that is labeled with that constant_expression.

If expression evaluates to a value that doesn't match any of the `case:` labels, and the `default:` label is present, control is transferred to the statement labeled with the `default:` label.

If expression evaluates to a value that doesn't match any of the `case:` labels, and the `default:` label is not present, none of the switch body is executed.

The break statement, when encountered anywhere in statement, exits the switch statement:

    switch(1) {
        case 1 : puts("1"); // prints "1",
        case 2 : puts("2"); // then prints "2" ("fall-through")
    }

    switch(1) {
        case 1 : puts("1"); // prints "1"
                 break;     // and exits the switch
        case 2 : puts("2");
                 break;
    }

As with all other selection and iteration statements, the switch statement establishes block scope: any identifier introduced in the expression goes out of scope after the statement.

If a VLA or another identifier with variably-modified type has a `case:` or a `default:` label within its scope, the entire switch statement must be in its scope (in other words, a VLA must be declared either before the entire switch or after the last label):

    switch (expr)
    {
        int i = 4; // not a VLA; OK to declare here
        f(i); // never called
    //  int a[i]; // error: VLA cannot be declared here
      case 0:
        i = 17;
    default:;
        int a[i]; // OK to declare VLA here
        printf("%d\n", i); // prints 17 if expr == 0, prints indeterminate value otherwise
    }

(since C99)

### Keywords

`switch`, `case`, `default`

### Example

Run this code

    #include <stdio.h>

    void func(int x)
    {
       printf("func(%d): ", x);
       switch(x)
       {
          case 1: printf("case 1, ");
          case 2: printf("case 2, ");
          case 3: printf("case 3.\n"); break;
          case 4: printf("case 4, ");
          case 5: printf("case 5, ");
          default: printf("default.\n");
       }
    }

    int main(void)
    {
       for(int i = 1; i < 10; ++i) func(i);
    }

Output:

    func(1): case 1, case 2, case 3.
    func(2): case 2, case 3.
    func(3): case 3.
    func(4): case 4, case 5, default.
    func(5): case 5, default.
    func(6): default.
    func(7): default.
    func(8): default.
    func(9): default.

### References

- C11 standard (ISO/IEC 9899:2011):

  - 6.8.4.2 The switch statement (p: 149-150)

- C99 standard (ISO/IEC 9899:1999):

  - 6.8.4.2 The switch statement (p: 134-135)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 3.6.4.2 The switch statement

### See also

C++ documentation for switch statement

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