Practice · Algorithm Design: Pseudocode, Flowcharts, and Tracing

Q1

Which property must every algorithm have?

A It must be written in Java. B It must terminate after a finite number of steps. C It must use at least one loop. D It must run in under one second.

Q2

In a flowchart, a decision is represented by a:

A rectangle B diamond C parallelogram D oval

Q3

Which flowchart symbol represents reading a value from the keyboard?

A Oval B Rectangle C Parallelogram D Diamond

Q4

The oval (rounded) symbol in a flowchart indicates:

A a calculation B the start or end of the algorithm C a decision D a loop body

Q5

How many flow lines leave a decision symbol in a standard flowchart?

A One B Two C Three D As many as needed

Q6

Which of the following is not one of the three fundamental control structures?

A Sequence B Selection C Recursion D Repetition

Q7

In pseudocode, total <- total + mark means:

A compare total with total + mark; B add mark to the current value of total and store the result in total; C declare a new variable total; D print the value of total + mark.

Q8

What is printed by this fragment?

a <- 4
b <- 7
a <- b
b <- a
print a, b

A 4 7 B 7 4 C 7 7 D 4 4

Q9

Which sequence correctly swaps the contents of x and y?

A x <- y; y <- x B t <- x; x <- y; y <- t C x <- x + y; y <- x D t <- x; y <- t; x <- y

Q10

Trace the fragment and give the output (/ is integer division).

count <- 0
n     <- 20
while n > 1 do
    n     <- n / 2
    count <- count + 1
endwhile
print count

A 4 B 5 C 6 D The loop never ends

Q11

What is the final value of sum?

sum <- 0
for i <- 1 to 5 do
    if i mod 2 = 0 then
        sum <- sum + i
    endif
endfor

A 6 B 9 C 15 D 10

Q12

Assume that for i <- 1 to 10 behaves like the equivalent while loop: i starts at 1, is tested against 10 before each pass and is increased by 1 at the end of each pass. After the loop finishes, the value of i is:

A 10 B 11 C 1 D undefined

Q13

A loop that must repeat exactly 30 times is best described as:

A sentinel-controlled B counter-controlled C flag-controlled D end-of-file controlled

Q14

You ask the user for marks and stop when the user types −1. This is:

A counter-controlled B sentinel-controlled C flag-controlled D query-controlled

Q15

Which value would be a bad choice of sentinel for a list of Celsius temperatures?

A −999 B 9999 C 0 D "END"

Q16

A boolean variable found, set inside a search loop and tested by the loop condition, implements:

A a flag-controlled loop B a counter-controlled loop C a nested loop D an infinite loop

Q17

Which fragment is an infinite loop?

A i <- 0; while i < 5 do i <- i + 1 endwhile B i <- 5; while i > 0 do i <- i - 1 endwhile C i <- 0; while i < 5 do print i endwhile D i <- 0; while i < 0 do i <- i + 1 endwhile

Q18

How many times does the inner body execute in total?

for i <- 1 to 4 do
    for j <- 1 to 3 do
        print i, j
    endfor
endfor

A 3 B 4 C 7 D 12

Q19

What is the output of this nested loop?

for i <- 1 to 3 do
    for j <- 1 to i do
        print "*"
    endfor
    newline
endfor

A A 3 by 3 block of nine stars B A right triangle with 1, 2 and 3 stars on successive lines C Three stars on one line D Six stars on one line

Q20

Where should the accumulator total be initialised to zero?

A Inside the loop body B Before the loop C After the loop D It does not need initialising

Q21

Consider average <- total / count. What must be checked before this statement?

A That total is positive. B That count is not zero. C That average has been declared. D Nothing needs to be checked.

Q22

What is the output?

x <- 1
while x <= 16 do
    print x
    x <- x * 2
endwhile

A 1 2 4 8 B 1 2 4 8 16 C 2 4 8 16 D 1 2 4 8 16 32

Q23

A loop whose body must execute at least once before the condition is tested is drawn with the decision:

A at the top of the loop B at the bottom of the loop C outside the loop D omitted

Q24

Which of these is a logic error rather than a notation error?

A Writing if x <- 5 where the convention requires =. B Computing the average inside the loop instead of after it. C Forgetting endif. D Misspelling while.

Q25

Stepwise refinement means:

A writing the program in one go and then fixing it; B breaking a problem into major steps and refining each until it can be coded directly; C rewriting pseudocode in Java line by line; D testing each loop separately.

Q26

What is printed?

n <- 5
result <- 1
while n > 0 do
    result <- result * n
    n <- n - 1
endwhile
print result

A 5 B 15 C 120 D 25

Q27

Which algorithm does the previous fragment implement?

A Sum of 1 to n B Factorial of n C Power of n D Greatest common divisor

Q28

What does this algorithm compute?

best <- first value
while more values remain do
    input v
    if v > best then best <- v endif
endwhile
print best

A The average B The smallest value C The largest value D The number of values

Q29

In a trace table, each row usually represents:

A one variable B one iteration of the loop C one output statement D one input value

Q30

Which change makes the loop print only the even numbers from 2 to 10?

A for i <- 2 to 10 step 2 B for i <- 1 to 5 C for i <- 1 to 10 step 1 D for i <- 10 to 2

Q31

What is the output?

count <- 0
for i <- 1 to 3 do
    for j <- 3 downto 1 do
        if i = j then count <- count + 1 endif
    endfor
endfor
print count

A 0 B 1 C 3 D 9

Q32

Off-by-one errors most often come from:

A using the wrong variable name; B confusing < with <= in the loop condition; C forgetting to print a result; D declaring a variable twice.

Q33

An algorithm is said to be definite when:

A it always terminates; B each of its steps has exactly one interpretation; C it produces at least one output; D it can be coded in any language.

Q34

Which statement about pseudocode is true?

A It must follow Java syntax exactly. B It is translated by a pseudocode compiler. C It expresses the logic of an algorithm independently of any programming language. D It cannot contain loops.

Q35 Short answer

Build a complete trace table for this fragment and state the output.

a <- 2
b <- 3
for k <- 1 to 3 do
    a <- a + b
    b <- b + 1
endfor
print a, b

Q36 Short answer

Write pseudocode that reads marks one at a time until the user enters −1, then prints how many marks were entered and their average. Use a sentinel-controlled loop and guard against division by zero.

Q37 Short answer

Describe, symbol by symbol, the flowchart of an algorithm that reads a number and prints whether it is positive, negative or zero.

Q38 Short answer

Explain the difference between a counter-controlled and a user-query loop, and give one situation where each is the better choice.

Q39 Programming

Translate your pseudocode from question 36 into a complete Java program. (If you have not yet studied Scanner and while loops, return to this question after Chapter 7.)