4.1.1.8 Random numbers and exception handling Quiz: AQA Computer Science, Unit 1

The 20 questions

1. What does random number generation in a program produce?

   • The same number every time the program runs, because the generator begins from a fixed starting point
   • Values chosen by a random process, not fixed in advance by the programmer
   • Only prime numbers, selected by a fixed rule that the programmer must supply each time
   • A memory address for each variable, which the operating system assigns when the program starts

2. A program needs a whole number between 1 and 6 inclusive, such as to simulate a die. Which description fits?

   • A constant value of 6, which is fixed and never changes between program runs
   • Random real number between 0 and 1, including fractional values such as 0.5
   • Random integer in the range 1 to 6
   • A Boolean value of TRUE or FALSE, which is used to decide the outcome of a test

3. What is an exception in programming?

   • A named constant with a fixed value
   • A standard statement that always runs in sequence
   • An unexpected event or error that interrupts normal execution
   • A type of loop that repeats forever

4. What is the purpose of exception handling?

   • To store values in binary files only, so that they can be read by other programs later
   • To remove the need for selection and iteration, so that the program runs in a single pass
   • To make every variable into a constant, so that no value can ever be changed by mistake
   • To detect an error and respond to it without the program crashing

5. Which language construct usually detects and handles an exception such as division by zero?

   • A string concatenation
   • A constant declaration
   • Try and catch blocks
   • A FOR loop with a fixed count

6. A program divides by a number entered by the user. Which action is most sensible if the user enters 0?

   • Store 0 as a constant and use that value in every later division in the program
   • Remove all selection from the program, so that no check is needed on the input value
   • Catch the exception and ask for a valid non-zero number
   • Multiply the result by zero, so that the division has a valid answer despite the error

7. A random integer generator is asked for a value between 10 and 20 inclusive. Which statement is correct?

   • Only the value 15 is returned, because the midpoint of the range is always selected
   • Values below 10 are returned about half the time, since the lower part of the range is favoured
   • Any integer from 10 to 20, including both ends, may be returned
   • Only real numbers are returned, because the generator cannot produce whole numbers

8. A program uses random numbers for a game. Which result is most likely to appear wrong to a player if the random generator is not called correctly?

   • No value at all, because the random generator is not allowed to be used in a game program
   • Random values that differ between runs, which is the expected behaviour of a generator
   • A value outside the requested range, caused by an off-by-one error in the generator's bounds
   • The same value repeating every time, which seems predictable

9. Which statement best describes why exception handling is needed when reading a number typed by a user?

   • The input might not be a valid number, so the program must catch the problem
   • Users cannot type numbers into a program, so the input must come from a file instead
   • Numbers typed by users are always invalid, so every entry must be rejected by the program
   • Exception handling replaces all variables, so that the program stores its data in exceptions

10. A random integer from 1 to 4 is generated, and one is added to it. What range of values is possible?

    • 1 to 4
    • 2 to 5
    • 0 to 4
    • 1 to 5

11. A simulation needs a random real number between 0 and 1. Which is the best description?

    • A string of digits such as 0.5, which must be converted before it can be used in sums
    • A Boolean value of TRUE or FALSE, which is used to decide the outcome of a yes-or-no test
    • Random real with a value from 0 up to but not including 1 (or up to 1)
    • Random integer of 0 or 1 only, which gives just two possible outcomes for each call

12. A program catches an exception but then continues with an unusable value. What is the main problem?

    • The exception handling has made the program faster
    • The exception has been stored as a constant
    • The program now uses too few variables
    • The handler does not recover the program state correctly

13. Which benefit does exception handling bring to a quiz program that reads a score as text?

    • It converts every score to a Boolean, so that only pass or fail results are ever stored
    • It removes the need for scores entirely, so the quiz only records whether each answer is correct
    • It makes the quiz run without any input, so that the scores are generated automatically by the system
    • It stops invalid input breaking the quiz and lets the user retry

14. A random number generator gives the value 3 on a call. Which statement about the next call is correct?

    • It must be 3 again because the generator has memory of the last value
    • It must be less than 3 always
    • It is not guaranteed to be 3, since each call is an independent selection
    • It must be 4

15. A program uses a random integer to pick one of 5 questions. Which range and index is used if the questions are stored from index 0?

    • Random integer from 0 to 5
    • Random integer from 0 to 4
    • Random integer from 1 to 5 only
    • Random real from 0 to 5

16. Which statement about exception handling is correct?

    • It is the same as a random number generator, because both produce values that are not predictable
    • It is only used for mathematical operations, such as division and square roots, and nothing else
    • It separates the normal code path from the code that responds to errors
    • It requires the program to stop before any error can occur, so that errors never reach the user

17. A program needs to simulate a fair coin. Which is most suitable?

    • A constant value of 1 that is always the same, which would give the same result each time
    • A string of length 10 that holds the words heads and tails in a fixed order each time
    • Random integer from 0 to 1, with 0 for heads and 1 for tails
    • Random real from 0 to 100, which gives a value that is then compared with 50 to decide heads

18. Why must a random number generator be used with a specified range rather than producing any value?

    • Because random values are always negative
    • So that the program no longer needs variables
    • Because random values can only be integers less than zero
    • So the output fits the needs of the program, such as valid indexes

19. A program uses random numbers and exception handling together. Which combination best describes its design?

    • The program avoids all selection and iteration
    • Random values are stored as constants and never change
    • Exceptions create random numbers in every loop
    • Random values drive behaviour while errors are caught and handled

20. What is the chance of a fair six-sided die giving a 6 on one roll?

    • 1 in 36
    • 1 in 2
    • 6 in 1
    • 1 in 6

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