Local variables

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Quick Questions

Shade in the A or B circle for each question.

1. Which line creates a local variable inside a subroutine?

A LOCAL Length INTEGER

B DECLARE Length : INTEGER

2. A variable is declared inside a procedure. Where can it be used?

A Only inside that procedure

B Anywhere in the whole program

3. PROCEDURE ShowArea() DECLARE Area : INTEGER Area ← 20 ENDPROCEDURE CALL ShowArea() OUTPUT Area What is wrong with the main program?

A Area should have been declared after ENDPROCEDURE

B Area is local to ShowArea, so the main program cannot use it

4. When does a local variable exist?

A Only while the subroutine is running

B For the whole time the program is running

5. Is a parameter in a subroutine local or global?

A Local to the subroutine

B Global to the whole program

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1DECLARE Total : INTEGER		AFUNCTION Double(N : INTEGER) RETURNS INTEGER DECLARE Result : INTEGER Result <- N * 2 RETURN Result ENDFUNCTION
2PROCEDURE ShowArea(Width : INTEGER)		BCount is declared outside the procedure in the main program, so it is not a local variable of Greet. DECLARE must be inside the procedure body.
3A local variable is declared inside the body of a function, before it is used		CWidth is a parameter, which is also a local variable that can only be used inside ShowArea
4A local variable is not available in the main program after the subroutine has finished		DCreates a local variable called Total inside a subroutine, which can only be used in that subroutine
5PROCEDURE Greet() OUTPUT Count ENDPROCEDURE DECLARE Count : INTEGER		ECALL ShowArea(5) OUTPUT Length
6CALL Calculate() OUTPUT Length		FLength is a local variable declared inside Calculate, so the main program cannot use it after the call.

Definitions

DECLARE

Fill in the Blanks

Complete each line of code by filling in the missing parts.

PROCEDURE ShowArea() _______ Length : INTEGER ENDPROCEDURE

PROCEDURE ShowPrice() DECLARE Price : ____ Price ← 2.5

PROCEDURE ShowLength() DECLARE Length : INTEGER Length _ 5

PROCEDURE Show(Width : INTEGER) OUTPUT _____ * 2 ENDPROCEDURE

PROCEDURE Show() DECLARE ____ : INTEGER Mark ← 80

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A PROCEDURE ShowArea()

B DECLARE Area INTEGER

C Area ← 5 * 4

D OUTPUT Area

E ENDPROCEDURE

Question 2

A PROCEDURE SetUp()

B DIM Count : INTEGER

C Count ← 0

D ENDPROCEDURE

Question 3

A PROCEDURE Hello()

B DECLARE Msg : STRING

C Msg = "Hi"

D OUTPUT Msg

E ENDPROCEDURE

Question 4

A PROCEDURE Show(N)

B DECLARE Temp : INTEGER

C Temp ← N * 2

D OUTPUT Temp

E ENDPROCEDURE

Question 5

A FUNCTION Age() RETURNS INTEGER

B DECLARE Years : INTEGER

C Yrs ← 15

D RETURN Years

E ENDFUNCTION

Answer Key

Local variables

Section A: Quick Questions

B — DECLARE Length : INTEGER

A — Only inside that procedure

B — Area is local to ShowArea, so the main program cannot use it

A — Only while the subroutine is running

A — Local to the subroutine

Section B: Match the Pairs

DECLARE Total : INTEGER → Creates a local variable called Total inside a subroutine, which can only be used in that subroutine

PROCEDURE ShowArea(Width : INTEGER) → Width is a parameter, which is also a local variable that can only be used inside ShowArea

A local variable is declared inside the body of a function, before it is used → FUNCTION Double(N : INTEGER) RETURNS INTEGER DECLARE Result : INTEGER Result <- N * 2 RETURN Result ENDFUNCTION

A local variable is not available in the main program after the subroutine has finished → CALL ShowArea(5) OUTPUT Length

PROCEDURE Greet() OUTPUT Count ENDPROCEDURE DECLARE Count : INTEGER → Count is declared outside the procedure in the main program, so it is not a local variable of Greet. DECLARE must be inside the procedure body.

CALL Calculate() OUTPUT Length → Length is a local variable declared inside Calculate, so the main program cannot use it after the call.

Section C: Definitions

DECLARE — Creates a local variable inside a procedure or function, e.g. DECLARE Length : INTEGER. It exists only while the subroutine runs and cannot be used in the main program.

Section D: Fill in the Blanks

PROCEDURE ShowArea()
   DECLARE Length : INTEGER
ENDPROCEDURE

PROCEDURE ShowPrice()
   DECLARE Price : REAL
   Price ← 2.5

PROCEDURE ShowLength()
   DECLARE Length : INTEGER
   Length ← 5

PROCEDURE Show(Width : INTEGER)
   OUTPUT Width * 2
ENDPROCEDURE

PROCEDURE Show()
   DECLARE Mark : INTEGER
   Mark ← 80

Section E: Spot the Error

B — A local variable is declared with DECLARE, a name, a colon and a data type. The colon is missing. It should be DECLARE Area : INTEGER.

B — DIM is not the pseudocode keyword for declaring a local variable. Inside a procedure it must be DECLARE Count : INTEGER.

C — Assignment in IGCSE pseudocode uses the arrow ←, not =. The line should be Msg ← "Hi".

A — A parameter is a local variable too, so it needs a data type in the header. It should be PROCEDURE Show(N : INTEGER).

C — Yrs was never declared in this function, so it does not exist as a local variable. The line should use the declared name: Years ← 15.