← IGCSE Computer Science Paper 2

Choosing the return data type of a function

Keyword in a function header, followed by a data type such as INTEGER, REAL, STRING or BOOLEAN. The value sent back by RETURN must be of that same type.

Part of: IGCSE Computer Science 0478 — 8.1c Procedures and Functions — Module 19

Understanding Choosing the return data type of a function in IGCSE Computer Science Paper 2

What it does: A count is always a whole number, so INTEGER is the type that matches the value sent back by RETURN. Text is stored as a STRING, so the header must say RETURNS STRING to match the text value returned. The type depends on the value being returned, not the parameter. A comparison gives TRUE or FALSE, so BOOLEAN is correct. The total is a number with decimal places, so it is REAL. STRING is for text.

Common mistakes: The function returns 15, which is a whole number, but the header says STRING. The header should say RETURNS INTEGER so it matches the value sent back. RETURN "Cost" sends back a STRING, but the header says RETURNS REAL. It should be RETURN Cost, which sends back the REAL value 4.5.

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This module's key terms are also in a printable crossword (Modules 409–418) and word search (Modules 399–418).

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Learning

Duo

A function calculates the average of three whole-number marks, which may include a decimal such as 72.5. Which header is best?

FUNCTION Average(a, b, c) RETURNS INTEGERFUNCTION Average(a, b, c) RETURNS REAL

Matches

FUNCTION IsPass(Mark : INTEGER) RETURNS INTEGER RETURN Mark >= 50 ENDFUNCTION

↓

The comparison Mark >= 50 gives TRUE or FALSE, which is a BOOLEAN, but the header says RETURNS INTEGER. It should be RETURNS BOOLEAN.

Applying

Meanings

Term

RETURNS

Meaning

Keyword in a function header, followed by a data type such as INTEGER, REAL, STRING or BOOLEAN. The value sent back by RETURN must be of that same type.

Practice

FUNCTION IsAdult(Age : INTEGER) RETURNS BOOLEAN

Testing

Gaps

FUNCTION Twice(N : INTEGER) RETURNS

Check Answer

Spots

1FUNCTION Age() RETURNS STRING

2 RETURN 15

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Quick Questions

1. A function calculates the average of three whole-number marks, which may include a decimal such as 72.5. Which header is best?

A. FUNCTION Average(a, b, c) RETURNS REAL ✓

B. FUNCTION Average(a, b, c) RETURNS INTEGER

An average can have a decimal part, so the RETURN value must be REAL. INTEGER can only hold whole numbers.

2. A function checks whether a password is long enough and sends back TRUE or FALSE. Which data type follows RETURNS?

A. RETURNS BOOLEAN ✓

B. RETURNS STRING

TRUE and FALSE are BOOLEAN values, so the header must say RETURNS BOOLEAN.

3. Which statement about RETURNS is correct?

A. The type after RETURNS can be any type, whatever value RETURN sends back.

B. The type after RETURNS must match the type of the value sent back by RETURN. ✓

The data type in the header is a promise. The value in the RETURN statement must be of that same type.

4. A function builds a greeting such as "Hello Sam" and sends it back. Which header is correct?

A. FUNCTION Greet(Name) RETURNS STRING ✓

B. FUNCTION Greet(Name) RETURNS BOOLEAN

Text such as "Hello Sam" is a STRING, so the function must be declared RETURNS STRING.

5. FUNCTION CountItems() RETURNS INTEGER RETURN "ten" ENDFUNCTION What is wrong with this function?

A. Nothing is wrong, because RETURN can send back any type.

B. It returns a STRING but the header says INTEGER, so the types do not match. ✓

"ten" is a STRING. The header promises an INTEGER, so this is a type mismatch. Return a whole number such as 10.

Match the Pairs

FUNCTION IsAdult(Age : INTEGER) RETURNS BOOLEAN → The function sends back a BOOLEAN, so RETURN must give TRUE or FALSE.

FUNCTION AverageMark(Total : INTEGER) RETURNS REAL → The function sends back a REAL, so RETURN must give a number that can have a decimal part.

A function that returns a whole number such as a count must have RETURNS INTEGER in its header. → FUNCTION CountItems() RETURNS INTEGER

A function that returns a piece of text such as a name must have RETURNS STRING in its header. → FUNCTION GetName() RETURNS STRING

FUNCTION IsPass(Mark : INTEGER) RETURNS INTEGER RETURN Mark >= 50 ENDFUNCTION → The comparison Mark >= 50 gives TRUE or FALSE, which is a BOOLEAN, but the header says RETURNS INTEGER. It should be RETURNS BOOLEAN.

FUNCTION GetGreeting() RETURNS INTEGER RETURN "Hello" ENDFUNCTION → The function returns the text "Hello", which is a STRING, but the header says RETURNS INTEGER. It should be RETURNS STRING.

Key Term

RETURNS

Keyword in a function header, followed by a data type such as INTEGER, REAL, STRING or BOOLEAN. The value sent back by RETURN must be of that same type.

Fill in the Blanks

1. FUNCTION Twice(N : INTEGER) RETURNS INTEGER RETURN N * 2 ENDFUNCTION

Hint: Type the data type that matches a whole number, because N * 2 gives a whole number when N is whole.

2. FUNCTION Half(N : INTEGER) RETURNS REAL RETURN N / 2 ENDFUNCTION

Hint: Type the data type for numbers with decimal places, because dividing with / can give a fractional result.

3. FUNCTION Grade(M : INTEGER) RETURNS STRING RETURN "Pass" ENDFUNCTION

Hint: Type the data type for text, because the RETURN line sends back a word in quotes.

4. FUNCTION IsEven(N : INTEGER) RETURNS BOOLEAN RETURN N MOD 2 = 0 ENDFUNCTION

Hint: Type the data type for a TRUE or FALSE value, because the expression after RETURN is a comparison.

5. FUNCTION NameLen(S : STRING) RETURNS INTEGER RETURN LENGTH(S) ENDFUNCTION

Hint: Type the data type that matches what LENGTH gives back (a count of characters), so the header does not return the wrong type.

Spot the Error

Question 1

A FUNCTION Age() RETURNS STRING

B RETURN 15

C ENDFUNCTION

D OUTPUT Age()

Line A — The function returns 15, which is a whole number, but the header says STRING. The header should say RETURNS INTEGER so it matches the value sent back.

Question 2

A FUNCTION Price() RETURNS REAL

B Cost ← 4.5

C RETURN "Cost"

D ENDFUNCTION

Line C — RETURN "Cost" sends back a STRING, but the header says RETURNS REAL. It should be RETURN Cost, which sends back the REAL value 4.5.

Question 3

A FUNCTION Name() RETURNS STRING

B DECLARE W : STRING

C W ← "Ava"

D RETURN LENGTH(W)

E ENDFUNCTION

Line D — LENGTH(W) gives an INTEGER, but the function is declared RETURNS STRING. It should be RETURN W so that a STRING is sent back.

Question 4

A FUNCTION Ok() RETURNS BOOLEAN

B Score ← 60

C RETURN Score

D ENDFUNCTION

Line C — Score is an INTEGER, but the header says RETURNS BOOLEAN. It should be RETURN Score >= 50, because a comparison gives TRUE or FALSE.

Question 5

A FUNCTION Avg() RETURNS INTEGER

B Total ← 7

C RETURN Total / 2

D ENDFUNCTION

Line A — 7 / 2 gives 3.5, which is a REAL value, so the header cannot say INTEGER. It should say RETURNS REAL.

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