WHILE ... DO ... ENDWHILE

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. When does a WHILE loop test its condition?

A Before each pass through the loop

B After each pass through the loop

2. Number ← 5 WHILE Number > 9 DO Number ← Number + 1 ENDWHILE How many times does the body run?

A At least once

B Zero times

3. A WHILE loop repeats its statements while the condition is...

A FALSE

B TRUE

4. Which line correctly closes a WHILE loop?

A ENDWHILE

B NEXT

5. Number ← 20 WHILE Number > 9 DO OUTPUT Number ENDWHILE What is wrong with this loop?

A Nothing in the body changes Number, so the loop never ends

B WHILE loops cannot use the > operator

Match the Pairs

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

Left column		Right column
1WHILE Number > 9 DO		AThe loop is closed with NEXT, which belongs to a FOR loop, instead of ENDWHILE
2ENDWHILE		BNothing in the body changes Number, so the condition stays TRUE and the loop never ends (an infinite loop)
3A WHILE loop tests its condition first, so if the condition starts FALSE the body runs zero times		CCloses the WHILE loop and sends control back to test the condition again
4Something inside the body must change the condition, or the loop never ends		DTests the condition before each pass and runs the loop body only while Number is greater than 9
5WHILE Number > 9 DO Count ← Count + 1 ENDWHILE		ENumber ← 5 WHILE Number > 9 DO OUTPUT Number ENDWHILE
6WHILE Number > 9 DO Number ← Number DIV 10 NEXT		FWHILE Number > 9 DO Number ← Number DIV 10 ENDWHILE

Definitions

WHILE ... DO ... ENDWHILE

Fill in the Blanks

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

_____ Number > 9 DO Number ← Number DIV 10 ENDWHILE

WHILE Count < 5 __ Count ← Count + 1 ENDWHILE

WHILE Number > 9 DO Number ← Number DIV 10 ________

WHILE Count < 5 DO OUTPUT Count _____ ← Count + 1

WHILE Lives _ 0 DO Lives ← Lives - 1 ENDWHILE

Spot the Error

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

Question 1

A Count ← 0

B WHILE Number > 9 DO

C Count = Count + 1

D Number ← Number DIV 10

E ENDWHILE

Question 2

A Count ← 0

B WHILE Count < 5 THEN

C OUTPUT Count

D Count ← Count + 1

E ENDWHILE

Question 3

A Number ← 100

B WHILE Number > 9 DO

C Number ← Number * 10

D ENDWHILE

E OUTPUT Number

Question 4

A Count ← 0

B WHILE Count < 3 DO

C Count ← Count + 1

D ENDIF

E OUTPUT Count

Question 5

A Total ← 0

B WHILE Total < 50 DO

C INPUT Value

D Total ← Value

E ENDWHILE

F OUTPUT Total

Answer Key

WHILE ... DO ... ENDWHILE

Section A: Quick Questions

A — Before each pass through the loop

B — Zero times

B — TRUE

A — ENDWHILE

A — Nothing in the body changes Number, so the loop never ends

Section B: Match the Pairs

WHILE Number > 9 DO → Tests the condition before each pass and runs the loop body only while Number is greater than 9

ENDWHILE → Closes the WHILE loop and sends control back to test the condition again

A WHILE loop tests its condition first, so if the condition starts FALSE the body runs zero times → Number ← 5 WHILE Number > 9 DO OUTPUT Number ENDWHILE

Something inside the body must change the condition, or the loop never ends → WHILE Number > 9 DO Number ← Number DIV 10 ENDWHILE

WHILE Number > 9 DO Count ← Count + 1 ENDWHILE → Nothing in the body changes Number, so the condition stays TRUE and the loop never ends (an infinite loop)

WHILE Number > 9 DO Number ← Number DIV 10 NEXT → The loop is closed with NEXT, which belongs to a FOR loop, instead of ENDWHILE

Section C: Definitions

WHILE ... DO ... ENDWHILE — A loop that tests its condition before each pass and repeats its statements while the condition is TRUE. It may run zero times, and the body must change the condition.

Section D: Fill in the Blanks

WHILE Number > 9 DO
    Number ← Number DIV 10
ENDWHILE

WHILE Count < 5 DO
    Count ← Count + 1
ENDWHILE

WHILE Number > 9 DO
    Number ← Number DIV 10
ENDWHILE

WHILE Count < 5 DO
    OUTPUT Count
    Count ← Count + 1

WHILE Lives > 0 DO
    Lives ← Lives - 1
ENDWHILE

Section E: Spot the Error

C — = is used for comparison, not for storing a value. Assignment must use the arrow, so the line should be Count ← Count + 1.

B — A WHILE loop header ends with DO, not THEN. THEN belongs to IF statements. It should be WHILE Count < 5 DO.

C — The body must change the variable so the condition eventually becomes FALSE. Multiplying makes Number bigger, so Number > 9 stays TRUE forever. It should be Number ← Number DIV 10.

D — A WHILE loop is closed with ENDWHILE. ENDIF closes an IF statement, so line 4 should be ENDWHILE.

D — This overwrites Total each pass instead of adding to it, so the total never builds up and the loop may never end. It should be Total ← Total + Value.