IBDP Computer Science B2.4 Programming algorithms HL Paper 1 - New Syllabus

(a) Three advantages of using sub-programs are:

• Modularity: The program can be divided into smaller, easier-to-understand parts, making the overall program easier to organize.

• Independent development: Each sub-program can be developed, tested and debugged independently, allowing the four students to work on different parts at the same time.

• Code reuse: A sub-program can be called multiple times, reducing duplication and making the program easier to maintain.

Other valid advantages include easier debugging, clearer program structure, reduced code size and easier maintenance when a sub-program needs to be changed.

(b) The input must be repeatedly requested until a value between 1 and 25 inclusive is entered. One valid pseudocode solution is:

inputInRange()

    K = input('Enter a number: ')

    loop while (K < 1) or (K > 25)
        output('The number is not in the range 1 to 25.')
        output('Please try again.')
        K = input('Enter a number: ')
    end loop

    output('Your number is valid.')
    return K

end inputInRange()

The loop continues while the input is outside the valid range. Once \(1 \leq K \leq 25\), the value is returned.

(c) The FLAGS array has 25 elements indexed from 0 to 24. Each value in MAT is used to determine an index in FLAGS. Since the numbers are from 1 to 25, the index is calculated as MAT[R][C] - 1.

isCorrectlyCompleted(MAT)

    // FLAGS contains 25 values indexed from 0 to 24
    // initialize FLAGS
    loop K from 0 to 24
        FLAGS[K] = 0
    end loop

    // match the values in MAT with indexes in FLAGS
    loop R from 0 to 4
        loop C from 0 to 4
            INDEX = MAT[R][C] - 1
            FLAGS[INDEX] = 1
        end loop
    end loop

    // inspect all elements in FLAGS
    F = true

    loop K from 0 to 24
        if FLAGS[K] = 0
            then F = false
        end if
    end loop

    if F = true
        then
            output('The table has been completed correctly')
        else
            output('The table has not been completed correctly')
    end if

end isCorrectlyCompleted()

The algorithm works because every number from 1 to 25 must occur exactly once. If a number is missing, its corresponding element in FLAGS remains \(0\), so the table is identified as incomplete.

Alternative valid approach: Count the number of \(1\) values in FLAGS. If the count is \(25\), output that the table has been completed correctly; otherwise, output that it has not been completed correctly.