AP CA A Unit 4 Review

What is output to the screen by the following code?

• 2 1 0 3 2 1 0 3 2 1

• 1 0 3 2 1 0 3 2 1 0

• 1 0 3 2 1 0 3 2 1

• 1 2 3 0 1 2 3 0 1 2

Answer explanation

This has the correct number of iterations and the correct pattern

Assuming that s is a correctly initialized String (that does not end in a space) which of the following best describes what the algorithm below does?

• Prints the number of times a space appears in str.

• Prints the character after each space in str.

• Prints the character before each space in str

• Prints each character in str followed by a space.

Answer explanation

The indexOf function returns the index of the first appearance of a character. For each iteration the character in str after this is printed, then str is replaced by everything after that space. This continues until indexOf (“ “) returns -1 when there are no spaces left

What is output by the following code?

• saopmoee

• saompoeel

• aspoomee

• Nothing is printed because there is an out of bounds error

Answer explanation

The code iterates forwards through str1 (“awesome”) starting at s and backwards through str2 (“leopard”) starting at a. It starts printing a character from str1 then str2 going back and forth until st1 runs out of letters in which case the loop ends.

Which of the following statements will return a random odd number between 5 and 15 inclusive?

• 2 * (int) (6 * Math.random()) + 5

• 2 * (int) (6 * Math.random() + 5)

• (int) (2 * 5 * Math.random() + 5)

• 2 * (int) (5 * Math.random()) + 5

Answer explanation

This is correct. The Math.random() method returns a random double between 0, inclusive and 1 exclusive. Therefore 6 * Math.random() will return a random double which is greater than or equal to 0 and smaller than 6. When this is cast to an int, the nearest integer value below will be returned. Therefore (int) (6 * Math.random()) will be an int between 0 and 5 inclusive. Multiplying this by 2 ensures every other number is printed: 2 * (int) (6 * Math.random()) returns a random number between 0, 2, 4, 6, 8 or 10 inclusive, and then shifting by 5 creates the values 5, 7, 9, 11, 13, 15

Set the following for loop header so that it prints the numbers, 10 5 0 -5 -10.

• 10, > -10, -= 5

• 10, >= -10, -= 5

• -10, <= 10, ++

• 10, > 10, -= 5

Answer explanation

i starts as 10, decreases by 5 each time, and no longer runs once the value of i is less than -10, so 10 5 0 -5 and -10 are printed

What does short circuit evaluation mean in the following code?

• if a >= b is false it evaluates c != d

• if a >= b is false it doesn't evaluate c != d

• if a >= b is true it evaluates c != d

• c != d is evaluated first, and if true it evaluates a >= b

Answer explanation

This is correct and is how short circuit evaluations works in an && expression (Short-circuit evaluation means that when evaluating boolean expressions (logical AND and OR ) you can stop as soon as you find the first condition which satisfies or negates the expression.)

-Explanation of why option if a >= b is true it evaluates c != d is wrong: Even though this is true, it does not represent short circuit evaluation and how it works.

For which of the following replacements for /* missing condition */ will the segment result in an infinite loop? (May choose more than one)

• I. a > 0

• II. a == 12

• III. a % 3 != 5

Answer explanation

Both of these conditions will result in an infinite loop

I - Since a starts at 5, which is great than 0, and because a is increased each time through the loop, it will always be greater than 0, this will result in an infinite loop, but it is not the only condition to cause an infinite loop

II - This will actually result in a loop that never runs

III - Since a value of a % 3 can only equal 0, 1 or 2, regardless of what the value of a is increased to, it will never equal 5, so the loop will always run, but is is not the only condition to cause an infinite loop

Which of the following code segments will print all the multiples of 5 between 1 and 100, not including 100? (May choose more than one)

• 
• 
• 

Answer explanation

I, II and III This is all correct. All values correctly print multiples of 5 up to but not including 100.

I ➜ Code segment I iterates through every integer k between 1 and 100, and uses the value of the expression k % 5 (this returns the remainder when k is divided by 5) to determine if each value of k is a multiple of 5, and prints it if so. But it is not the only for loop that works as intended.

II ➜ Code segment II begins with a value of k = 5, prints the value of k and increases it by 5 each time, ensuring it is still a multiple of 5, until it is greater than or equal to 100. But it is not the only for loop that works as intended.

III➜ Code segment III iterates through every integer k, starting at 1 all the way through 19. It prints 5 * k, which must be a multiple of 5 each time. But it is not the only for loop that works as intended.

Assume that x and y are boolean variables and have been properly initialized

• Always true

• Always false

• true only when x and y have the same value

• true only when x and y have different values

Answer explanation

No matter the boolean values, the whole expression evaluates to true

What is output when the program runs?

• 
• 
• 
• 

Answer explanation

This is correct, the outer loop specifies what value is printed and the inner loop specifies how many times it is printed