Error: variable not set to zero first

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Quick Questions

Shade in the A or B circle for each question.

1. A program adds up 10 marks in a FOR loop but never sets Total to 0 first. What is the problem?

A Total starts from an unknown value, so the final answer may be wrong

B Total will always end as 0 because it was never set

2. Which line correctly prepares a variable to count how many students passed?

A Count = 0

B Count ← 0

3. Where should Total ← 0 be placed in a program that adds numbers in a loop?

A Inside the loop, on the first line of the body

B Before the loop starts

4. FOR Index ← 1 TO 5 / Total ← 0 / Total ← Total + Number / NEXT Index. What happens?

A Total is reset to 0 each repeat, so it only holds the last number

B Total correctly holds the sum of all five numbers

5. A program counts how many scores are above 50, but Count ← 0 is missing before the loop. Which statement is true?

A Count may start at an unknown value, so the final count could be wrong

B Count will start at 1 automatically, so only a small error occurs

Match the Pairs

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

Left column		Right column
1Total ← 0		ASets the total to 0 before the loop so it starts from a known value
2Count ← 0		BCount ← 0 WHILE Count < 10 DO Count ← Count + 1 ENDWHILE
3Correct: set the total to 0 once, before the loop starts		CTotal ← 0 FOR Index ← 1 TO 5 INPUT Num Total ← Total + Num NEXT Index
4Correct: set the counter to 0 before the loop so it is not reset each time		DSets the counter to 0 before the loop so it counts from zero
5FOR Index ← 1 TO 5 INPUT Num Total ← Total + Num NEXT Index		ETotal is never set to 0 before the loop, so it starts from an unknown value. Fix: add Total ← 0 before the FOR line.
6FOR Index ← 1 TO 5 Count ← 0 Count ← Count + 1 NEXT Index		FCount ← 0 is inside the loop, so it resets every time and always ends as 1. Fix: move Count ← 0 above the loop.

Definitions

Total ← 0

Fill in the Blanks

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

Total ← _ FOR Index ← 1 TO 5

_____ ← 0 WHILE Num <> 0 DO Count ← Count + 1

Total ← 0 ___ Index ← 1 TO 5 Total ← Total + Num

Count ← _ REPEAT Count ← Count + 1

Total _ 0 WHILE Total < 20 DO Total ← Total + 5

Spot the Error

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

Question 1

A Total ← Total

B INPUT Price

C WHILE Price <> -1 DO

D Total ← Total + Price

E INPUT Price

F ENDWHILE

Question 2

A INPUT Limit

B DECLARE Count : INTEGER

C Count ← Count + 1

D WHILE Count < Limit DO

E Count ← Count + 1

F ENDWHILE

Question 3

A Total ← 0

B DECLARE Count : INTEGER

C WHILE Total < 100 DO

D Total ← Total + 20

E Count ← Count + 1

F ENDWHILE

Question 4

A Total ← 0

B FOR Index ← 1 TO 5

C INPUT Mark

D Total ← 0 + Mark

E NEXT Index

F OUTPUT Total

Question 5

A Count ← 0

B REPEAT

C Count ← 0 + 1

D INPUT Number

E UNTIL Number = 0

F OUTPUT Count

Answer Key

Error: variable not set to zero first

Section A: Quick Questions

A — Total starts from an unknown value, so the final answer may be wrong

B — Count ← 0

B — Before the loop starts

A — Total is reset to 0 each repeat, so it only holds the last number

A — Count may start at an unknown value, so the final count could be wrong

Section B: Match the Pairs

Total ← 0 → Sets the total to 0 before the loop so it starts from a known value

Count ← 0 → Sets the counter to 0 before the loop so it counts from zero

Correct: set the total to 0 once, before the loop starts → Total ← 0 FOR Index ← 1 TO 5 INPUT Num Total ← Total + Num NEXT Index

Correct: set the counter to 0 before the loop so it is not reset each time → Count ← 0 WHILE Count < 10 DO Count ← Count + 1 ENDWHILE

FOR Index ← 1 TO 5 INPUT Num Total ← Total + Num NEXT Index → Total is never set to 0 before the loop, so it starts from an unknown value. Fix: add Total ← 0 before the FOR line.

FOR Index ← 1 TO 5 Count ← 0 Count ← Count + 1 NEXT Index → Count ← 0 is inside the loop, so it resets every time and always ends as 1. Fix: move Count ← 0 above the loop.

Section C: Definitions

Total ← 0 — Set a total or counter to 0 before the loop. If you forget, it starts from an unknown value; if you put it inside the loop, it resets every time.

Section D: Fill in the Blanks

Total ← 0
FOR Index ← 1 TO 5

Count ← 0
WHILE Num <> 0 DO
  Count ← Count + 1

Total ← 0
FOR Index ← 1 TO 5
  Total ← Total + Num

Count ← 0
REPEAT
  Count ← Count + 1

Total ← 0
WHILE Total < 20 DO
  Total ← Total + 5

Section E: Spot the Error

A — Total ← Total does not set the total to 0. It copies an unknown starting value, so every later sum is wrong. It must be Total ← 0 before the loop.

C — Count is used on the right-hand side before it has been given a value, so it starts from an unknown value. Line 3 must be Count ← 0 to set the counter before the loop.

B — DECLARE only creates the variable. It does not give Count a value, so it starts from an unknown value. It must be Count ← 0 before the loop.

D — Using 0 inside the loop resets the total on every repeat, so it only holds the last mark. The loop must add to the running total: Total ← Total + Mark, with Total ← 0 once before the loop.

C — Resetting the counter inside the loop means Count is always 1, however many numbers are entered. The loop line must be Count ← Count + 1. The 0 belongs before the loop.