STEP in a FOR loop

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Quick Questions

Shade in the A or B circle for each question.

1. Which loop counts DOWN from 10 to 1?

A FOR Count <- 10 TO 1

B FOR Count <- 10 TO 1 STEP -1

2. FOR Number <- 0 TO 100 STEP 10 What values does Number take?

A 0, 10, 20, ... 100

B 0, 1, 2, ... 100

3. A FOR loop has no STEP. How much does the counter change each repeat?

A It goes up by 1

B It goes up by 0

4. How many times does this loop repeat? FOR Number <- 0 TO 100 STEP 10

A 11 times

B 10 times

5. Which STEP value makes the counter count down?

A STEP 1

B STEP -1

Match the Pairs

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

Left column		Right column
1FOR Number <- 0 TO 100 STEP 10		ACounts down from 10 to 1, taking away 1 each repeat, giving 10 repeats
2FOR Count <- 10 TO 1 STEP -1		BSTEP must be followed directly by the step value. The extra = sign is not valid in Cambridge pseudocode.
3If STEP is left out, the counter goes up by 1 each repeat		CCounts up in tens: 0, 10, 20 and so on up to 100, giving 11 repeats
4A negative STEP is needed when the start value is bigger than the end value		DFOR Lap <- 8 TO 2 STEP -2
5FOR Count <- 10 TO 1 OUTPUT Count NEXT Count		EFOR Index <- 1 TO 5
6FOR Number <- 0 TO 100 STEP = 10		FThere is no STEP -1, so the counter goes up by 1 by default. The start (10) is already past the end (1), so the loop body never runs.

Definitions

FOR Count <- 10 TO 1 STEP -1

Fill in the Blanks

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

FOR Number <- 0 TO 100 ____ 10 OUTPUT Number NEXT Number

FOR Count <- 10 TO 1 STEP __ OUTPUT Count NEXT Count

// Outputs 0, 20, 40, 60, 80, 100 FOR Number <- 0 TO 100 STEP __ NEXT Number

// Same as having no STEP at all FOR Index <- 1 TO 10 STEP _ NEXT Index

// Repeats 6 times: 0, 10, 20, 30, 40, 50 FOR Count <- 0 TO __ STEP 10 NEXT Count

Spot the Error

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

Question 1

A FOR Count <- 10 TO 1 STEP -1

B OUTPUT Count

C ENDFOR

Question 2

A DECLARE Num : INTEGER

B OUTPUT "Counting down"

C FOR Num <- 10 TO 1

D OUTPUT Num

E NEXT Num

Question 3

A OUTPUT "Evens"

B FOR Num <- 2 TO 10 STEP 2

C OUTPUT Num

D NEXT Count

Question 4

A DECLARE Count : INTEGER

B FOR Count <- 10 TO 0 STEP 2

C OUTPUT Count

D NEXT Count

Question 5

A Total <- 0

B FOR Num <- 0 TO 100 STEP 10

C Total <- Total + Num

D NEXT Num STEP 10

E OUTPUT Total

Answer Key

STEP in a FOR loop

Section A: Quick Questions

B — FOR Count <- 10 TO 1 STEP -1

A — 0, 10, 20, ... 100

A — It goes up by 1

A — 11 times

B — STEP -1

Section B: Match the Pairs

FOR Number <- 0 TO 100 STEP 10 → Counts up in tens: 0, 10, 20 and so on up to 100, giving 11 repeats

FOR Count <- 10 TO 1 STEP -1 → Counts down from 10 to 1, taking away 1 each repeat, giving 10 repeats

If STEP is left out, the counter goes up by 1 each repeat → FOR Index <- 1 TO 5

A negative STEP is needed when the start value is bigger than the end value → FOR Lap <- 8 TO 2 STEP -2

FOR Count <- 10 TO 1 OUTPUT Count NEXT Count → There is no STEP -1, so the counter goes up by 1 by default. The start (10) is already past the end (1), so the loop body never runs.

FOR Number <- 0 TO 100 STEP = 10 → STEP must be followed directly by the step value. The extra = sign is not valid in Cambridge pseudocode.

Section C: Definitions

FOR Count <- 10 TO 1 STEP -1 — STEP sets how much the FOR counter changes each repeat. Without STEP the counter goes up by 1. A negative STEP, such as -1, makes the counter count down.

Section D: Fill in the Blanks

FOR Number <- 0 TO 100 STEP 10
  OUTPUT Number
NEXT Number

FOR Count <- 10 TO 1 STEP -1
  OUTPUT Count
NEXT Count

// Outputs 0, 20, 40, 60, 80, 100
FOR Number <- 0 TO 100 STEP 20
NEXT Number

// Same as having no STEP at all
FOR Index <- 1 TO 10 STEP 1
NEXT Index

// Repeats 6 times: 0, 10, 20, 30, 40, 50
FOR Count <- 0 TO 50 STEP 10
NEXT Count

Section E: Spot the Error

C — A FOR loop in Cambridge pseudocode ends with NEXT followed by the counter name, not ENDFOR. Line 3 should be NEXT Count.

C — Without STEP the counter goes up by 1, so it can never count down from 10 to 1 and the loop would not run. It needs STEP -1: FOR Num <- 10 TO 1 STEP -1.

D — NEXT must name the same counter as the FOR line. The counter is Num, so line 4 should be NEXT Num.

B — The counter starts at 10 and must go down to 0, so the STEP has to be negative. A positive STEP 2 would move away from 0. It should be STEP -2.

D — STEP belongs on the FOR line only. The NEXT line just names the counter, so line 4 should be NEXT Num.