← IGCSE Computer Science Paper 2

Local variables

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.

Part of: IGCSE Computer Science 0478 — 8.1c Procedures and Functions — Module 26

Understanding Local variables in IGCSE Computer Science Paper 2

What it does: Result is declared with DECLARE inside the function body, so it is local to Double and exists only while Double runs. A local variable is created when the subroutine is called and stops existing when the subroutine ends. This is different from a global variable. Parameters are local to their subroutine, so Width cannot be used in the main program.

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

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This module's key terms are also in a printable crossword (Modules 419–428) and word search (Modules 419–438).

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Learning

Duo

Which line creates a local variable inside a subroutine?

DECLARE Length : INTEGERLOCAL Length INTEGER

Matches

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.

Applying

Meanings

Term

DECLARE

Meaning

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.

Practice

PROCEDURE CalcTotal(Price : INTEGER)

Testing

Gaps

Length : INTEGER

Check Answer

Spots

1PROCEDURE ShowArea()

2 DECLARE Area INTEGER

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Quick Questions

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

A. LOCAL Length INTEGER

B. DECLARE Length : INTEGER ✓

In Cambridge pseudocode, a variable is created with DECLARE name : TYPE. Written inside a procedure or function body, it becomes a local variable.

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

A. Only inside that procedure ✓

B. Anywhere in the whole program

A local variable can only be used inside the subroutine where it was declared. The main program cannot see it.

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 ✓

Area exists only inside ShowArea. Using it in the main program causes an error because it is not available there.

4. When does a local variable exist?

A. Only while the subroutine is running ✓

B. For the whole time the program is running

A local variable is created when the subroutine is called and stops existing when the subroutine ends. This is different from a global variable.

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

A. Local to the subroutine ✓

B. Global to the whole program

Parameters are also local. For example, in PROCEDURE Greet(Name : STRING), Name can only be used inside Greet.

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.

Key Term

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.

Fill in the Blanks

1. PROCEDURE ShowArea() DECLARE Length : INTEGER ENDPROCEDURE

Hint: Type the keyword that creates a local variable inside a subroutine

2. PROCEDURE ShowPrice() DECLARE Price : REAL Price ← 2.5

Hint: Type the data type used for numbers with decimal places

3. PROCEDURE ShowLength() DECLARE Length : INTEGER Length ← 5

Hint: Type the assignment symbol that stores a value in the local variable

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

Hint: A parameter is also local. Type its name to use it inside the procedure

5. PROCEDURE Show() DECLARE Mark : INTEGER Mark ← 80

Hint: Type the name of the local variable that is given a value on the next line

Spot the Error

Question 1

A PROCEDURE ShowArea()

B DECLARE Area INTEGER

C Area ← 5 * 4

D OUTPUT Area

E ENDPROCEDURE

Line 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.

Question 2

A PROCEDURE SetUp()

B DIM Count : INTEGER

C Count ← 0

D ENDPROCEDURE

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

Question 3

A PROCEDURE Hello()

B DECLARE Msg : STRING

C Msg = "Hi"

D OUTPUT Msg

E ENDPROCEDURE

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

Question 4

A PROCEDURE Show(N)

B DECLARE Temp : INTEGER

C Temp ← N * 2

D OUTPUT Temp

E ENDPROCEDURE

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

Question 5

A FUNCTION Age() RETURNS INTEGER

B DECLARE Years : INTEGER

C Yrs ← 15

D RETURN Years

E ENDFUNCTION

Line 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.

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