AP CS A Unit 6 Quiz PRACTICE

Assume you have the following array: int[] num = {3, 2, 8, 1, 7}; How would you decrement (subtract) the second element in the array by one?

• 2--

• 1--;

• num[1]--;

• num[2]--;

• num[1]++;

Answer explanation

The second element of num has index of 1 and the -- subtracts 1 from the value accessed by the []

Consider the following code: double[] list = new double[25]; The index of the first value is ______ and the last index is ______.

Answer explanation

The first element of an array always has index 0, meaning that the 25th and final element of this array must have index 24, one less than the number of elements in the array.

What data types can a standard array not hold?

• ints

• booleans

• doubles

• Strings

• All the data types can be in a standard array

Answer explanation

All primitive data types + Strings can be stored in a standard array

Consider the code shown here. What is output?

• 24

• 26

• 28

• 36

• 38

Answer explanation

The i % 2 == 0 will pick every even indexed value and then will sum them together, 2, 8, 12, 16 are those values and sum to 38

Consider the following code, intended to search an array for a value and print the position where that value was found.

What could replace /* Missing Code */ so that the code works as intended?

• number[i] = location;

• location = numbers[i];

• location = i;

• i = location;

• location = 1;

Answer explanation

In a linear search, we need to find the index in the array where the value we are searching for is stored. The missing code runs when we have found the value, so we need to store the index of that value in the found variable.

The following is intended to count the number of times the number 100 is found in an array of test scores.

Which of the following could replace /* Missing Code */ so that the code works as intended?

• tests[i] == 100

• tests == 100

• tests != 100

• tests.equals(100)

• tests[i].equals(100)

Answer explanation

The loop should check one value in the array on each pass through the loop, and check whether it is equal to 100.

Consider the following code, intended to count the number of words in the array with a length greater than or equal to 5.

What could be used to replace /* Missing Code */ so that the code works as intended?

• vocab.length[i]() >= 5

• vocab[i].length() >= 5

• vocab.length() > 5

• vocab[i].length() > 5

• vocab.length() >= 6

Answer explanation

The loop should check one value in the array on each pass through the loop, and check whether its length is greater than or equal to 5.

Consider the following code.

What is output?

• 3

• 4

• 6

• 7

• None of the above

Answer explanation

This loop counts the number of words in the String array where “e” appears in the substring of the last three letters of the word. This occurs in seven of the words.

The following is intended to return the location of the first instance of the String the user enters from the keyboard, -1 if not found.

Which of the following could replace /* Missing Code */ so that it works as intended?

• !search.equals(names[i])

• search.equals(names[i])

• search[i].equals(names[i])

• search != names[i]

• search.equals(names)

Answer explanation

This compares the string search to the String at index i.

Consider the following method, hasRepeats, which is intended to return true if an array of Strings contains the same value more than once and false otherwise.

Which of the following should be used to replace /* missing code */ so that hasRepeats works as intended?

• int j = 0; j < k + 1; j++

• int j = 0; j < arr.length; j++

• int j = k; j < arr.length; j++

• int j = k + 1; j < arr.length - k; j++

• int j = k + 1; j < arr.length; j++

Answer explanation

int j = k + 1; j < arr.length; j++ is correct. Currently the outer if loop goes through each element in the array in turn by increasing the index k. The inner loop should go through the array up to the end to see if any of the elements in the array match the array at index k. It should begin with the first element after k, since if it begins at an index less than this, it will repeat checking each pair of variables twice, and more importantly end up comparing the value of the element at index k with itself, which would return true.