Robust & Secure Programming (AQA GCSE Computer Science)

Figure 7 shows part of a program written in Python.

Figure 7

validChoice = False
while validChoice == False:
   choice = int(input('Enter your choice [1 - 10]'))
   if choice >= 1 and choice <= 10:
     validChoice = True
   else:
     print('Invalid choice')
print('Valid choice')

Complete the following test plan for the code shown in Figure 7.

State the line number from the program in Figure 8 which contains the error that stops the program from sometimes working correctly

Figure 8

1 num1 = int(input())
2 num2 = int(input())
3 hcf = 1
4 count = 1
5 while count < num1:
6    if (num1 % count == 0 and num2 % count == 0):
7      hcf = count
8    count = count + 1
9 print(hcf)

Describe one way that the program in Figure 3 could be made more robust.

Figure 3

def calculate(width, length, height):
  if height == -1:
     return width * length
  else:
     return width  length  height

numOne = int(input("Enter width: "))
numTwo = int(input("Enter length: "))
numThree = int(input("Enter height, –1 to ignore: "))

answer = calculate(numOne, numTwo, numThree)

if numThree == -1:
  print(f"Area {answer}")
else:
  print(f"Volume {answer}")

Figure 9

1 names ← ['Natalie', 'Alex', 'Roshana']
2 scores ← [78, 81, 72, 27, 51, 54, 52, 55, 59]
3 count ← 0
4 FOR i ← 0 TO 2
5     person ← names[i]
6     OUTPUT 'Student: ', person
7     FOR j ← 0 TO 1
8         OUTPUT j + 1
9         result ← scores[i * 3 + j]
10        OUTPUT result
11        count ← count + 1
12    ENDFOR
13 ENDFOR

How could the error in the algorithm in Figure 9 be corrected?

Identify one choice

Figure 10 shows part of an algorithm that has been written in pseudocode.

There is an error in the algorithm.

The algorithm should:

• get the start year and end year from the user

• check that the start year is before the end year

• check that the start year is before 2000

• calculate the difference between the two years after a valid start year has been entered.
  

• Line numbers are included but are not part of the algorithm.

Figure 10

1 validChoice ← False
2 REPEAT
3    difference ← –1
4    OUTPUT 'Enter a start year '
5    startYear ← USERINPUT
6    OUTPUT 'Enter an end year '
7    endYear ← USERINPUT
8    IF startYear ≥ endYear THEN
9      OUTPUT 'Start year must be before end year'
10    ELSE
11     IF startYear < 2000 THEN
12        OUTPUT 'Start year must be before 2000'
13     ELSE
14        validChoice ← True
15     ENDIF
16    ENDIF
17 UNTIL validChoice = True
18 difference ← endYear - startYear
19 OUTPUT difference

Table 1 shows three tests used to check the algorithm in Figure 10.

Complete the table to show what the values of the validChoice and difference variables would be for the given test data.

Table 1

The algorithm in Figure 10 contains a logic error on line 11.

Describe how the error on line 11 can be corrected.