Procedures and Functions

Example — A cinema charges £8.50 for a standard seat and £14.00 for a premium seat.

Write a function TicketPrice that takes the size of the group and the chosen seat type as inputs, then returns the total amount to pay.

FUNCTION TicketPrice(GroupSize : INTEGER, SeatType : STRING) RETURNS REAL
   DECLARE CostPerSeat : REAL
   IF SeatType = "premium" THEN
      CostPerSeat ← 14.00
   ELSE
      CostPerSeat ← 8.50
   ENDIF
   RETURN GroupSize * CostPerSeat
ENDFUNCTION

// Using the function
OUTPUT TicketPrice(2, "standard")    // outputs 17.00
OUTPUT TicketPrice(3, "premium")     // outputs 42.00

Key features of this answer that earn marks:

• The header uses FUNCTION ... RETURNS REAL (returns a number with a decimal part).
• The parameters GroupSize and SeatType are declared with data types.
• A local variable CostPerSeat is used to hold the looked-up price.
• The RETURN statement gives back the calculated total.
• The function is called inside an expression (here, OUTPUT), not with CALL.

The same calculation written as a procedure would not return a value; instead it would output the cost directly. The function version is more useful because the caller can do other things with the returned value (display it, save it, add a booking fee, etc.).