The arithmetic expression in the case head is evaluated. If the resulting value is not an integer, it is integerized by rounding.

The integer value is used as an index into the list of statements in the case body. The N statements in the case body are numbered 0 to N–1. The statement corresponding to the index value is the statement executed. If the index value is less than zero or greater than N–1, the program is discontinued with a fault.