Count-controlled loop: FOR … TO … NEXT

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Quick Questions

Shade in the A or B circle for each question.

1. Which line correctly starts a loop that runs 30 times using Index?

A FOR Index ← 1 TO 30

B FOR Index = 1 TO 30 DO

2. Which line correctly closes the loop that began FOR Index ← 1 TO 30?

A ENDFOR Index

B NEXT Index

3. In FOR Index ← 1 TO 30, how does Index change after each repeat?

A It increases by 1 each time

B It stays at 1 until the loop ends

4. Where do the statements that repeat belong?

A Written after NEXT Index

B Indented between FOR and NEXT

5. Which NEXT line matches FOR Index ← 1 TO 30?

A NEXT Index

B NEXT Count

Match the Pairs

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

Left column		Right column
1FOR Index ← 1 TO 30		AThe statement inside the loop is not indented. The body should be indented, as in ' OUTPUT Index', so it is clear which lines repeat.
2NEXT Index		BCloses the loop, adds 1 to Index and goes back to the FOR line
3The statements inside the loop are indented so you can see which lines repeat on each pass		CFOR Index ← 1 TO 30 OUTPUT Index NEXT Index
4A loop that runs 30 times, with Index going up by 1 each time, from 1 to 30		DFOR Index ← 1 TO 30
5FOR Index ← 1 TO 30 OUTPUT Index NEXT Count		EStarts a loop that repeats the indented statements once for each value of Index, from 1 up to 30
6FOR Index ← 1 TO 30 OUTPUT Index NEXT Index		FNEXT uses a different name (Count) from the loop variable Index. NEXT must repeat the same variable name as the FOR line, so it should be NEXT Index.

Definitions

FOR Index ← 1 TO 30

Fill in the Blanks

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

___ Index ← 1 TO 30 Scores[Index] ← 0 NEXT Index

FOR Index ← 1 __ 30 OUTPUT Scores[Index] NEXT Index

FOR Index ← 1 TO 30 OUTPUT Scores[Index] NEXT _____

FOR Index ← 1 TO 30 Total ← Total + Scores[Index] ____ Index

FOR Index _ 1 TO 30 Scores[Index] ← 0 NEXT Index

Spot the Error

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

Question 1

A FOR Index ← 1 TO 30

B Score[Count] ← 0

C NEXT Index

Question 2

A FOR Index ← 1 TO 10

B OUTPUT Mark[Index

C NEXT Index

Question 3

A FOR Index ← 1 TO 5

B INPUT Num[Index]

C NEXT Num

Question 4

A Total ← 0

B FOR Index ← 1 TO 30

C Total ← Total + Mark[Index]

D ENDFOR

Question 5

A FOR Index = 1 TO 30

B Mark[Index] ← 0

C NEXT Index

Answer Key

Count-controlled loop: FOR … TO … NEXT

Section A: Quick Questions

A — FOR Index ← 1 TO 30

B — NEXT Index

A — It increases by 1 each time

B — Indented between FOR and NEXT

A — NEXT Index

Section B: Match the Pairs

FOR Index ← 1 TO 30 → Starts a loop that repeats the indented statements once for each value of Index, from 1 up to 30

NEXT Index → Closes the loop, adds 1 to Index and goes back to the FOR line

The statements inside the loop are indented so you can see which lines repeat on each pass → FOR Index ← 1 TO 30 OUTPUT Index NEXT Index

A loop that runs 30 times, with Index going up by 1 each time, from 1 to 30 → FOR Index ← 1 TO 30

FOR Index ← 1 TO 30 OUTPUT Index NEXT Count → NEXT uses a different name (Count) from the loop variable Index. NEXT must repeat the same variable name as the FOR line, so it should be NEXT Index.

FOR Index ← 1 TO 30 OUTPUT Index NEXT Index → The statement inside the loop is not indented. The body should be indented, as in ' OUTPUT Index', so it is clear which lines repeat.

Section C: Definitions

FOR Index ← 1 TO 30 — A count-controlled loop. It repeats the indented statements once for each value of Index, from 1 up to 30, going up by 1 each time. NEXT Index closes the loop.

Section D: Fill in the Blanks

FOR Index ← 1 TO 30
    Scores[Index] ← 0
NEXT Index

FOR Index ← 1 TO 30
    OUTPUT Scores[Index]
NEXT Index

FOR Index ← 1 TO 30
    OUTPUT Scores[Index]
NEXT Index

FOR Index ← 1 TO 30
    Total ← Total + Scores[Index]
NEXT Index

FOR Index ← 1 TO 30
    Scores[Index] ← 0
NEXT Index

Section E: Spot the Error

B — The array index must use the loop variable Index, which changes each time round. Count is not the loop variable. It should be Score[Index] ← 0.

B — The closing square bracket is missing. The statement inside the loop should be OUTPUT Mark[Index].

C — NEXT must repeat the loop variable name from the FOR line. Num is the array, not the loop variable. It should be NEXT Index.

D — In IGCSE pseudocode a FOR loop is closed with NEXT followed by the loop variable, not ENDFOR. It should be NEXT Index.

A — The loop variable is given its start value with the assignment arrow ←, not =. It should be FOR Index ← 1 TO 30.