One-dimensional arrays in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers.

C++

int arr[[1]];

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

A5

B10

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as size which creates an empty array.

Forgetting to specify the size.

The array size must be specified as 5 to create an array with 5 elements.

2fill in blank

medium

Complete the code to assign the value 10 to the first element of the array.

C++

arr[[1]] = 10;

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

A5

B0

C1

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the first index.

Using negative indices which are invalid.

Array indexing in C++ starts at 0, so the first element is at index 0.

3fill in blank

hard

Fix the error in the code to correctly print the third element of the array.

C++

std::cout << arr[[1]] << std::endl;

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

A3

B0

C1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 which is the fourth element.

Using index 1 which is the second element.

The third element is at index 2 because indexing starts at 0.

4fill in blank

hard

Fill both blanks to create an array of 4 integers and assign 7 to its last element.

C++

int arr[[1]];
arr[[2]] = 7;

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

A4

B3

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 4 which is out of bounds.

Using size 5 instead of 4.

The array size is 4, so the last element is at index 3 (4 - 1).

5fill in blank

hard

Fill all three blanks to initialize an array with values 1, 2, 3 and print the second element.

C++

int arr[[1]] = {1, 2, 3};
std::cout << arr[[2]] << std::endl;
int size = [3];

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

A3

B1

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong size for the array.

Using wrong index to print the second element.

The array size is 3, the second element is at index 1, and size is 3.

Practice

1. What is the starting index of a one-dimensional array in C++?

easy

A. -1

B. 1

C. 0

D. Depends on the array size

Solution

1. Step 1: Understand array indexing in C++

   Arrays in C++ always start indexing from 0, meaning the first element is at index 0.

2. Step 2: Confirm the index range

   Indexes go from 0 up to size-1, so the first index is always 0 regardless of array size.

3. Final Answer:

   0 -> Option C

4. Quick Check:

   Array indexing starts at 0 [OK]

Hint: Remember: C++ arrays always start at zero index [OK]

Common Mistakes:

• Thinking arrays start at 1
• Assuming negative indexes are valid
• Confusing with other languages

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

easy

A. array<int> arr(5);

B. int arr(5);

C. int arr = new int[5];

D. int arr[5];

Solution

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

   In C++, a fixed-size array is declared using square brackets with size: int arr[5];

2. Step 2: Check other options for correctness

   int arr(5); uses parentheses which is invalid for arrays. array<int> arr(5); uses incorrect syntax (not standard array). int arr = new int[5]; uses dynamic allocation syntax but is incorrect without pointer.

3. Final Answer:

   int arr[5]; -> Option D

4. Quick Check:

   Fixed-size arrays use square brackets [OK]

Hint: Use square brackets [] to declare fixed-size arrays [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Confusing with vector syntax
• Incorrect dynamic allocation syntax

3. What will be the output of the following code?

int arr[4] = {10, 20, 30, 40};
std::cout << arr[2];

medium

A. 30

B. 20

C. 40

D. Compilation error

Solution

1. Step 1: Identify the array elements and indexes

   The array arr has elements: arr[0]=10, arr[1]=20, arr[2]=30, arr[3]=40.

2. Step 2: Access the element at index 2

   arr[2] is 30, so std::cout will print 30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   arr[2] = 30 [OK]

Hint: Remember array index starts at 0, so arr[2] is third element [OK]

Common Mistakes:

• Confusing index 2 with 1 or 3
• Expecting output 20 or 40
• Thinking code causes error

4. Identify the error in the following code snippet:

int arr[3] = {1, 2, 3};
for(int i = 0; i <= 3; i++) {
    std::cout << arr[i] << " ";
}

medium

A. Missing semicolon after array declaration

B. Loop runs one time too many, causing out-of-bounds access

C. Syntax error in for loop declaration

D. Array size is incorrect, should be 4

Solution

1. Step 1: Analyze the loop range and array size

   The array has size 3 with valid indexes 0,1,2. The loop runs from i=0 to i=3 inclusive, which means 4 iterations.

2. Step 2: Identify out-of-bounds access

   When i=3, arr[3] is accessed, which is outside the array bounds and causes undefined behavior.

3. Final Answer:

   Loop runs one time too many, causing out-of-bounds access -> Option B

4. Quick Check:

   Loop index must be less than array size [OK]

Hint: Loop index must be less than array size, not less or equal [OK]

Common Mistakes:

• Using <= instead of <
• Assuming array size is 4
• Ignoring out-of-bounds errors

5. Given an integer array arr of size n, which code snippet correctly calculates the sum of all elements?

hard

A. int sum = 0;
for(int i = 0; i < n; i++) sum += arr[i];

B. int sum = 0;
for(int i = 1; i < n; i++) sum += arr[i];

C. int sum = 0;
for(int i = 0; i <= n; i++) sum += arr[i];

D. int sum = arr[0];
for(int i = 1; i < n; i++) sum = arr[i];

Solution

1. Step 1: Understand correct loop bounds for array traversal

   Array indexes go from 0 to n-1, so loop must run i from 0 to less than n.

2. Step 2: Check each option for correctness

   int sum = 0; for(int i = 1; i < n; i++) sum += arr[i]; starts from 1, missing arr[0]. int sum = 0; for(int i = 0; i <= n; i++) sum += arr[i]; uses <= n, causing out-of-bounds access. int sum = 0; for(int i = 0; i < n; i++) sum += arr[i]; correctly sums all elements from 0 to n-1. int sum = arr[0]; for(int i = 1; i < n; i++) sum = arr[i]; overwrites sum instead of adding.

3. Final Answer:

   int sum = 0; for(int i = 0; i < n; i++) sum += arr[i]; -> Option A

4. Quick Check:

   Loop from 0 to n-1 sums all elements [OK]

Hint: Loop from 0 to less than n to cover all elements [OK]

Common Mistakes:

• Starting loop at 1
• Using <= n causing errors
• Overwriting sum instead of adding