Choosing between CASE and IF

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. A program reads a menu choice of 1, 2 or 3 and runs a different action for each. Which structure fits best?

A CASE Choice OF

B Three separate IF statements that each test ranges

2. A program converts a mark into a grade: A for 80 or more, B for 60 to 79, C for 40 to 59. Which structure fits best?

A CASE Mark OF

B IF ... THEN ... ELSE

3. Which condition CANNOT be handled neatly by a CASE statement?

A 1: OUTPUT "Start game"

B IF Age >= 13 AND Score > 50 THEN

4. Which line is a correct case in a CASE statement for a menu?

A 2: OUTPUT "Load game"

B 2 TO 4: OUTPUT "Load game"

5. A user types a letter: 'S' to save, 'L' to load, 'Q' to quit. Which should you use?

A CASE Letter OF

B IF Letter > 'A' AND Letter < 'Z' THEN

Match the Pairs

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

Left column		Right column
1CASE OF Choice		AIF Age >= 16 AND HasTicket = TRUE THEN
2IF Mark >= 70 THEN		BTests one variable, Choice, against several single values such as 1, 2 or 3, like a menu
3A menu where the user picks 1, 2 or 3 is one variable tested against single values, so use CASE		CCASE OF Choice 1 : OUTPUT "Play" 2 : OUTPUT "Quit" ENDCASE
4A condition that combines two variables cannot be written as a CASE, so use IF		DTests a range of values, so IF is used rather than CASE, as in grade boundaries
5CASE OF Mark 70 TO 100 : Grade ← "A" ENDCASE		EGrade boundaries are ranges, so CASE is the wrong choice. Use IF Mark >= 70 THEN instead.
6IF Choice = 1 THEN OUTPUT "Play" ELSE IF Choice = 2 THEN OUTPUT "Quit" ENDIF ENDIF		FA menu tests one variable against single values, so CASE OF Choice is clearer than long nested IF statements.

Definitions

CASE OF

Fill in the Blanks

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

____ Choice OF 1 : OUTPUT "Play" ENDCASE

CASE Choice __ 2 : OUTPUT "Quit" ENDCASE

IF Mark __ 70 THEN OUTPUT "Merit" ENDIF

IF Age >= 13 ___ Score > 50 THEN OUTPUT "Pass" ENDIF

CASE Choice OF 3 : OUTPUT "Help" _______

Spot the Error

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

Question 1

A INPUT Choice

B CASE OF Choice

C 1 TO 2 : OUTPUT "Play"

D 2 : OUTPUT "Quit"

E ENDCASE

Question 2

A IF Mark >= 70 THEN

B Grade ← "A"

C OTHERWISE

D Grade ← "B"

E ENDIF

Question 3

A INPUT Choice

B CASE OF Choice

C 1 : OUTPUT "Play"

D 2 OUTPUT "Quit"

E ENDCASE

Question 4

A INPUT Pct

B IF Pct >= 40 AND < 60 THEN

C OUTPUT "Merit"

D ENDIF

Question 5

A INPUT Option

B CASE Option OF

C 1 : OUTPUT "Open"

D 2 : OUTPUT "Save"

E ENDCASE

Answer Key

Choosing between CASE and IF

Section A: Quick Questions

A — CASE Choice OF

B — IF ... THEN ... ELSE

B — IF Age >= 13 AND Score > 50 THEN

A — 2: OUTPUT "Load game"

A — CASE Letter OF

Section B: Match the Pairs

CASE OF Choice → Tests one variable, Choice, against several single values such as 1, 2 or 3, like a menu

IF Mark >= 70 THEN → Tests a range of values, so IF is used rather than CASE, as in grade boundaries

A menu where the user picks 1, 2 or 3 is one variable tested against single values, so use CASE → CASE OF Choice 1 : OUTPUT "Play" 2 : OUTPUT "Quit" ENDCASE

A condition that combines two variables cannot be written as a CASE, so use IF → IF Age >= 16 AND HasTicket = TRUE THEN

CASE OF Mark 70 TO 100 : Grade ← "A" ENDCASE → Grade boundaries are ranges, so CASE is the wrong choice. Use IF Mark >= 70 THEN instead.

IF Choice = 1 THEN OUTPUT "Play" ELSE IF Choice = 2 THEN OUTPUT "Quit" ENDIF ENDIF → A menu tests one variable against single values, so CASE OF Choice is clearer than long nested IF statements.

Section C: Definitions

CASE OF — Use CASE OF to test one variable against single values, like a menu choice. Use IF for ranges, like grade boundaries, or when conditions combine several variables.

Section D: Fill in the Blanks

CASE Choice OF
    1 : OUTPUT "Play"
ENDCASE

CASE Choice OF
    2 : OUTPUT "Quit"
ENDCASE

IF Mark >= 70 THEN
    OUTPUT "Merit"
ENDIF

IF Age >= 13 AND Score > 50 THEN
    OUTPUT "Pass"
ENDIF

CASE Choice OF
    3 : OUTPUT "Help"
ENDCASE

Section E: Spot the Error

C — Each CASE branch tests one single value, like a menu choice. A range such as 1 TO 2 needs an IF statement. It should be 1 : OUTPUT "Play".

C — OTHERWISE belongs only in a CASE statement. An IF statement uses ELSE for the other branch.

D — Each CASE value must be followed by a colon before its statement. It should be 2 : OUTPUT "Quit".

B — A range needs IF with a full condition on each side of AND. The variable must be repeated: Pct >= 40 AND Pct < 60.

B — The CASE header is written CASE OF followed by the variable being tested. It should be CASE OF Option.