GCSE Computer Science Paper 2 B: Computational Thinking, Algorithms and Programming

Splitting a problem into parts is decomposition. Keeping only the details that matter is abstraction.

With indexes 0 to 8, the middle is index 4, which is 25. 52 is larger, so the search continues in indexes 5 to 8, whose middle is index 6, 40. 52 is larger again, so it continues in 7 to 8, whose middle is index 7, which holds 52.

A linear search works on a list in any order, whereas a binary search only works on a sorted list.

6 and 2 swap, 6 and 9 stay, 9 and 4 swap, 9 and 1 swap: 2, 6, 4, 1, 9. The largest value has moved to the end.

The list is split in half, then in half again, until there are four lists of one item: 6, 2, 9 and 4. Neighbouring lists are merged in order, giving 2, 6 and 4, 9. Those two lists are then merged by repeatedly comparing their front items and taking the smaller, giving 2, 4, 6, 9.

Whole numbers are integers, money is real, yes or no is Boolean, 10B is a string because it has more than one character, and a single letter is a character.

17 divided by 5 is 3 remainder 2, so MOD gives 2 and DIV gives 3. 2 to the power 4 is 16.

int() casts a string to an integer.

Each pass adds i x 2: 0 + 2 = 2, 2 + 4 = 6, 6 + 6 = 12, and 12 is printed.

A local variable is declared inside a subroutine and can only be used there; it disappears when the subroutine ends. A global variable is declared in the main program and can be used anywhere in it.

P is 1 whenever C is 0. When C is 1, P is only 1 if A and B are both 1, which is the last row.

AND needs both inputs to be 1.

Q = S AND (D OR W). The brackets matter: without them S AND D OR W would sound whenever a window opened.

1 AND 0 is 0, NOT 0 is 1, and 1 OR 0 is 1.

Minimum characters is a length check, a pattern is a format check, limits are a range check, and not blank is a presence check.

Defensive design means planning for misuse: anticipating how users might enter unexpected or malicious data and making sure the program copes rather than crashing or giving wrong results. Examples are validating every input, and authentication so only allowed users can use the program.

5 is typical valid data, 10 is at the edge of the range, 11 is the right type but out of range, and ten is the wrong type of data.

A compiler translates everything first and produces an executable; an interpreter translates and runs line by line.

Error diagnostics highlight the line where a syntax error is and say what is wrong, so the programmer goes straight to it. Breakpoints pause the running program at a chosen line, so the programmer can step through it line by line and watch the variables change, which is how logic errors are found.

Check the bands in order with if, elif and else, using < 16 and < 65 so that 16 and 65 fall in the right band.

def ticketPrice(age):
    if age < 16:
        return 5.50
    elif age < 65:
        return 8.00
    else:
        return 6.00

Validate with a while loop, then loop once per ticket, adding ticketPrice(age) to a running total.

def ticketPrice(age):
    if age < 16:
        return 5.50
    elif age < 65:
        return 8.00
    else:
        return 6.00

tickets = int(input("How many tickets? "))
while tickets < 1 or tickets > 10:
    tickets = int(input("Enter a number from 1 to 10: "))
total = 0
for i in range(tickets):
    age = int(input("Age: "))
    total = total + ticketPrice(age)
print("Total cost:", total)

Line 02 uses > 4, so a group of exactly 4 misses out. It should be >= 4.

if members >= 4:

Row 0, seat 3 is the last item of the first row, B. Row 2, seat 3 is the last item of the last row, F.

Two nested loops visit every seat, counting those that hold F.

def countFree(seats):
    free = 0
    for row in seats:
        for seat in row:
            if seat == "F":
                free = free + 1
    return free

Check the seat first. Only a free seat is changed; a booked one just gets the message.

def bookSeat(seats, row, seat):
    if seats[row][seat] == "F":
        seats[row][seat] = "B"
        print("Booked")
    else:
        print("Already taken")

The 2D list only exists in RAM while the program runs, so every booking would be lost when the program closes or the computer restarts. Saving it to a file on secondary storage keeps the bookings permanently, so they can be loaded the next time the program starts.

Inputs: the member's ID, and the number of tickets they have bought. Output: the number of free tickets they have earned.

Integer division by 10, DIV in OCR Exam Reference Language, // in Python, counts the complete tens.

def freeTickets(bought):
    return bought // 10