Linear search and bubble sort

Find one mark, then order the list

• Syllabus topic 10.2 asks for two algorithms on an array: a linear search and a bubble sort.
• A linear search looks at every cell. Remember the index when the value matches. If it never matches, the index stays 0.
• Searching does not move the values. Sorting does.

DECLARE Values : ARRAY[1:4] OF INTEGER
DECLARE I, Pos : INTEGER
Values[1] ← 4
Values[2] ← 9
Values[3] ← 1
Values[4] ← 7
Pos ← 0
FOR I ← 1 TO 4
    IF Values[I] = 9 THEN
        Pos ← I
    ENDIF
NEXT I
OUTPUT Pos

Bubble the largest to the end

• Compare each pair of neighbours. When the left one is larger, swap them through a temporary variable.
• One comparison is not the whole sort. Repeat the pass until every pair has been handled.
• For four values, an outer loop of three passes and an inner loop across the pairs is enough.

DECLARE Score : ARRAY[1:4] OF INTEGER
DECLARE I, J, Temp : INTEGER
Score[1] ← 4
Score[2] ← 1
Score[3] ← 3
Score[4] ← 2
FOR I ← 1 TO 3
    FOR J ← 1 TO 3
        IF Score[J] > Score[J + 1] THEN
            Temp ← Score[J]
            Score[J] ← Score[J + 1]
            Score[J + 1] ← Temp
        ENDIF
    NEXT J
NEXT I
OUTPUT Score[1]
OUTPUT Score[2]
OUTPUT Score[3]
OUTPUT Score[4]

Common mistakes

• A swap needs three assignments. Copying the right cell over the left one loses the left value.
• THEN stays on the IF line in this guide. The inner NEXT names J, the outer names I.

Now you try

• First report where 9 sits. Then sort four values into ascending order, one per line.

Independent transfer

The final task has no supplied algorithm. Plan its inputs, processing and outputs, then solve it before opening support. Check more than the sample case.