Library routines inside your own subroutines

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Quick Questions

Shade in the A or B circle for each question.

1. Your function IsEven must use a library routine to test for an even number. Which RETURN line is correct?

A RETURN Number DIV 2 = 0

B RETURN Number MOD 2 = 0

2. Can a function you write call a library routine such as ROUND inside its own statements?

A Yes: RETURN ROUND(Price, 2) uses the value that ROUND gives back

B No: only the main program can call ROUND

3. Which header is correct for IsEven, which uses MOD to test a whole number?

A FUNCTION IsEven(Number : INTEGER) RETURNS BOOLEAN

B FUNCTION IsEven(Number : INTEGER) RETURNS INTEGER

4. Inside RoundPrice, which statement rounds Price to 2 decimal places and gives it back?

A RETURN ROUND(2, Price)

B RETURN ROUND(Price, 2)

5. FUNCTION RollDie RETURNS INTEGER must give a whole number from 1 to 6. Which RETURN line fits?

A RETURN ROUND(RANDOM() * 5, 0) + 1

B RETURN RANDOM() * 6

Match the Pairs

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

Left column		Right column
1RETURN Number MOD 2 = 0		AOUTPUT ROUND(CalculateTotal(Price), 2)
2RETURN ROUND(Price * 1.1, 2)		BFUNCTION RollDie() RETURNS INTEGER RETURN ROUND(RANDOM() * 5, 0) + 1 ENDFUNCTION
3A function called RollDie uses the RANDOM library routine and returns a whole number from 1 to 6		CThe result of ROUND is not returned. The function must use RETURN so the rounded value is passed back to the caller.
4A user-defined function is used beside a library routine in one statement, by passing the function's result into ROUND		DDIV is used instead of MOD. DIV gives the whole-number quotient, not the remainder, so the test does not check whether the number is even.
5FUNCTION IsEven(Number : INTEGER) RETURNS BOOLEAN RETURN Number DIV 2 = 0 ENDFUNCTION		EInside IsEven, this uses MOD to find the remainder after dividing by 2 and returns TRUE when the remainder is 0
6FUNCTION RoundPrice(Price : REAL) RETURNS REAL ROUND(Price, 2) ENDFUNCTION		FInside a function, this works out the price plus 10 percent and returns it rounded to 2 decimal places

Definitions

RETURN ROUND(Price, 2)

Fill in the Blanks

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

FUNCTION IsEven(N : INTEGER) RETURNS BOOLEAN RETURN N ___ 2 = 0 ENDFUNCTION

FUNCTION RollDie() RETURNS INTEGER RETURN ROUND(______() * 5, 0) + 1 ENDFUNCTION

FUNCTION Tidy(Price : REAL) RETURNS REAL RETURN ROUND(Price, _) ENDFUNCTION

Result ← _____(AddTax(Price), 2) OUTPUT Result

FUNCTION Tens(N : INTEGER) RETURNS INTEGER RETURN N ___ 10 ENDFUNCTION

Spot the Error

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

Question 1

A FUNCTION Roll RETURN INTEGER

B RETURN ROUND(RANDOM()*5,0)+1

C ENDFUNCTION

Question 2

A PROCEDURE Fix(P) RETURNS REAL

B RETURN ROUND(P, 2)

C ENDFUNCTION

Question 3

A FUNCTION Fix(P) RETURNS REAL

B NewP ← ROUND(P, 2)

C RETURN P

D ENDFUNCTION

Question 4

A Num ← 14

B IF IsEven THEN

C OUTPUT "Even"

D ENDIF

Question 5

A PROCEDURE ShowTime(Secs)

B Mins ← Secs MOD 60

C OUTPUT Mins

D ENDPROCEDURE

Answer Key

Library routines inside your own subroutines

Section A: Quick Questions

B — RETURN Number MOD 2 = 0

A — Yes: RETURN ROUND(Price, 2) uses the value that ROUND gives back

A — FUNCTION IsEven(Number : INTEGER) RETURNS BOOLEAN

B — RETURN ROUND(Price, 2)

A — RETURN ROUND(RANDOM() * 5, 0) + 1

Section B: Match the Pairs

RETURN Number MOD 2 = 0 → Inside IsEven, this uses MOD to find the remainder after dividing by 2 and returns TRUE when the remainder is 0

RETURN ROUND(Price * 1.1, 2) → Inside a function, this works out the price plus 10 percent and returns it rounded to 2 decimal places

A function called RollDie uses the RANDOM library routine and returns a whole number from 1 to 6 → FUNCTION RollDie() RETURNS INTEGER RETURN ROUND(RANDOM() * 5, 0) + 1 ENDFUNCTION

A user-defined function is used beside a library routine in one statement, by passing the function's result into ROUND → OUTPUT ROUND(CalculateTotal(Price), 2)

FUNCTION IsEven(Number : INTEGER) RETURNS BOOLEAN RETURN Number DIV 2 = 0 ENDFUNCTION → DIV is used instead of MOD. DIV gives the whole-number quotient, not the remainder, so the test does not check whether the number is even.

FUNCTION RoundPrice(Price : REAL) RETURNS REAL ROUND(Price, 2) ENDFUNCTION → The result of ROUND is not returned. The function must use RETURN so the rounded value is passed back to the caller.

Section C: Definitions

RETURN ROUND(Price, 2) — Your own subroutine can call a library routine such as ROUND, MOD, DIV or RANDOM in its statements and use the value it gives back, for example in a RETURN.

Section D: Fill in the Blanks

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

FUNCTION RollDie() RETURNS INTEGER
  RETURN ROUND(RANDOM() * 5, 0) + 1
ENDFUNCTION

FUNCTION Tidy(Price : REAL) RETURNS REAL
  RETURN ROUND(Price, 2)
ENDFUNCTION

Result ← ROUND(AddTax(Price), 2)
OUTPUT Result

FUNCTION Tens(N : INTEGER) RETURNS INTEGER
  RETURN N DIV 10
ENDFUNCTION

Section E: Spot the Error

A — The keyword in a function header is RETURNS, not RETURN. The header should be FUNCTION Roll RETURNS INTEGER.

A — A procedure does not return a value. The subroutine uses RETURN with ROUND, so it must be a FUNCTION.

C — This returns the original price and ignores the rounded value. It should be RETURN NewP so the result of ROUND is sent back.

B — IsEven needs the number to test in brackets when it is called. It should be IF IsEven(Num) THEN.

B — MOD gives the remainder, not the number of whole minutes. Whole minutes need DIV: Mins ← Secs DIV 60.