Why arrays are needed in C++ - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers.

C++

int numbers[[1]];

Drag options to blanks, or click blank then click option'

A0

B10

C5

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative numbers as size.

Forgetting the size inside the brackets.

The number inside the square brackets specifies the size of the array. Here, 5 means the array can hold 5 integers.

2fill in blank

medium

Complete the code to access the third element of the array named 'scores'.

C++

int thirdScore = scores[[1]];

Drag options to blanks, or click blank then click option'

A2

B1

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 instead of 2 for the third element.

Confusing 1-based and 0-based indexing.

Array indexes start at 0, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to correctly initialize an array with values 1 to 4.

C++

int arr[4] = {1, 2, 3, [1];

Drag options to blanks, or click blank then click option'

A5

B4

C0

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number outside the intended sequence.

Providing fewer or more values than the array size.

The array size is 4, so it must have exactly 4 values. The last value should be 4 to match the sequence 1, 2, 3, 4.

4fill in blank

hard

Fill both blanks to create an array of 3 floats and assign 2.5 to the first element.

C++

float [1][[2]];
[1][0] = 2.5;

Drag options to blanks, or click blank then click option'

Aprices

B3

C4

Dvalues

Attempts:

3 left

💡 Hint

Common Mistakes

Using a size that doesn't match the intended number of elements.

Using inconsistent variable names.

The array is named 'prices' and has size 3. Then we assign 2.5 to the first element at index 0.

5fill in blank

hard

Fill all three blanks to declare an array of 4 integers and set the last element to 10.

C++

int [1][[2]];
[1][[3]] = 10;

Drag options to blanks, or click blank then click option'

Adata

B4

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 4 instead of 3 for the last element.

Mismatch between array size and index.

The array named 'data' has size 4. The last element is at index 3 (since indexing starts at 0), so we assign 10 there.

Practice

1. Why do we need arrays in C++ programming?

easy

A. To perform mathematical calculations faster

B. To store only one value at a time

C. To store multiple values of the same type together

D. To create functions

Solution

1. Step 1: Understand the purpose of arrays

   Arrays group many values of the same type in one place, making data management easier.

2. Step 2: Compare with other options

   The other options do not describe the main purpose of arrays.

3. Final Answer:

   To store multiple values of the same type together -> Option C

4. Quick Check:

   Arrays store many values = A [OK]

Hint: Arrays hold many same-type values together [OK]

Common Mistakes:

• Thinking arrays store different types
• Confusing arrays with single variables
• Believing arrays speed up math automatically

2. Which of the following is the correct way to declare an array of 5 integers in C++?

easy

A. int arr[5];

B. int arr;

C. array int arr(5);

D. int arr = {5};

Solution

1. Step 1: Recall C++ array declaration syntax

   Arrays are declared by specifying type, name, and size in square brackets, like int arr[5];

2. Step 2: Check each option

   int arr[5]; matches correct syntax. int arr = {5}; attempts to initialize a single int, int arr; declares a single int, array int arr(5); is invalid syntax.

3. Final Answer:

   int arr[5]; -> Option A

4. Quick Check:

   Array declaration uses brackets = D [OK]

Hint: Use type name[size] to declare arrays [OK]

Common Mistakes:

• Missing brackets for size
• Using wrong keywords
• Trying to assign size like a value

3. What will be the output of this C++ code?

int arr[3] = {10, 20, 30};
std::cout << arr[1];

medium

A. 20

B. 30

C. 10

D. Compilation error

Solution

1. Step 1: Understand array indexing

   Arrays start at index 0, so arr[0] = 10, arr[1] = 20, arr[2] = 30.

2. Step 2: Identify the printed element

   The code prints arr[1], which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Remember array index starts at 0 [OK]

Common Mistakes:

• Assuming index starts at 1
• Confusing values at indexes
• Expecting syntax error

4. Find the error in this C++ code snippet:

int arr[3];
arr[3] = 50;

medium

A. Syntax error in declaration

B. No error

C. Missing semicolon

D. Array index out of bounds error

Solution

1. Step 1: Check array size and indexing

   Array arr has size 3, valid indexes are 0, 1, 2.

2. Step 2: Identify invalid index usage

   arr[3] accesses the fourth element, which is out of bounds and causes error.

3. Final Answer:

   Array index out of bounds error -> Option D

4. Quick Check:

   Index 3 invalid for size 3 array [OK]

Hint: Array indexes go from 0 to size-1 [OK]

Common Mistakes:

• Using index equal to size
• Ignoring out of bounds errors
• Confusing syntax errors with runtime errors

5. You want to store the daily temperatures for a week and calculate the average. Why is using an array a good choice here?

hard

A. Because arrays automatically calculate averages

B. Because arrays allow storing multiple related values with easy access by position

C. Because arrays can change size dynamically

D. Because arrays store values of different types together

Solution

1. Step 1: Understand the problem requirements

   We need to store multiple temperature values for each day and access them easily.

2. Step 2: Evaluate array features

   Arrays store multiple values of the same type and allow access by index, perfect for daily temperatures.

3. Step 3: Eliminate incorrect options

   Arrays do not calculate averages automatically, cannot change size dynamically, and store only one type.

4. Final Answer:

   Because arrays allow storing multiple related values with easy access by position -> Option B

5. Quick Check:

   Arrays store many values accessibly = A [OK]

Hint: Arrays group related data for easy access [OK]

Common Mistakes:

• Thinking arrays auto-calculate
• Believing arrays resize automatically
• Assuming arrays hold mixed types