The switch Statement

Description

The expression after the word switch is the controlling expression. The controlling expression must have integral type. The statement following the controlling expression is typically a compound statement. The compound statement is called the switch body.

The statements in the switch body may be labeled with case labels. The case label is followed by an integral constant expression and a colon. No two case constant expressions in the same switch statement may have the same value.

When the switch statement executes, integral promotions are performed on the controlling expression; the result is compared with the constant expressions after the case labels in the switch body. If one of the constant expressions matches the value of the controlling expression, control passes to the statement following that case expression.

If no expression matches the value of the control expression and a statement in the switch body is labeled with the default label, control passes to that statement. Only one statement of the switch body may be labeled the default. By convention, the default label is included last after the case labels, although this is not required by the C programming language.

If there is no default, control passes to the statement immediately following the switch body and the switch effectively becomes a no- operation statement.

The switch statement operates like a multiway else-if chain except the values in the case statements must be constant expressions, and, most importantly, once a statement is selected from within the switch body, control is passed from statement to statement as in a normal C program. Control may "fall" through to following case statements. Using a break statement is the most common way to leave a switch body. If a break statement is encountered, control passes to the statement immediately following the switch body.

Example

The following example shows a switch statement that includes several case labels. The program selects the case whose constant matches getchar.

  switch (getchar ( ) )
{
       case 'r':
       case 'R':
          moveright ( );
          break;
       case 'l':
       case 'L':
          moveleft ( );
          break;
       case 'B':
          moveback ( );
          break;
       case 'A':
       default:
          moveahead ( );
          break;
}