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Procedures, Functions, Arrays and File Handling: Question 1

Syllabus 8.1

Multiple choice 1 mark

A program uses a global variable, TicketsSold, and a procedure that declares its own local variable with the identical identifier, to record how many cinema tickets have been sold.

DECLARE TicketsSold : INTEGER
TicketsSold ← 10

PROCEDURE ResetCounter()
    DECLARE TicketsSold : INTEGER
    TicketsSold ← 0
    OUTPUT TicketsSold
ENDPROCEDURE

CALL ResetCounter()
OUTPUT TicketsSold

What is displayed, in order, by the two OUTPUT statements above?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Identify the two variables that share the identifier TicketsSold

The global TicketsSold is declared before any procedure, and its value is set to 10. The procedure ResetCounter then contains its own line DECLARE TicketsSold : INTEGER. This statement creates a brand-new, local variable that happens to have the same identifier as the global one, but it is a completely separate piece of storage that exists only while the procedure is running.

Step 2: Trace what happens inside the procedure

CALL ResetCounter() runs the procedure body:

  • DECLARE TicketsSold : INTEGER creates the local variable.
  • TicketsSold ← 0 sets this local variable to 0.
  • OUTPUT TicketsSold displays the local variable’s value: 0.

The global TicketsSold, still holding 10, is never touched by any of these three lines.

Step 3: Trace what happens after the procedure ends

Once ResetCounter finishes running, its local TicketsSold is destroyed. Control returns to the main program, where the identifier TicketsSold now refers to the global variable again. Since the procedure only ever changed its own local copy, the global variable is unaffected and still holds 10, so OUTPUT TicketsSold displays 10.

Final answer

  • First OUTPUT (inside the procedure): 0
  • Second OUTPUT (after the procedure call finishes): 10
  • Displayed, in order: 0 then 10, option B