Array Declaration and Initialization in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an integer array named 'numbers' of size 5.

DSA C

int numbers[[1]];

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

A10

B5

C0

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as size which is invalid.

Using a variable name instead of a number without declaration.

The code declares an integer array 'numbers' with 5 elements.

2fill in blank

medium

Complete the code to initialize the array 'scores' with values 10, 20, 30.

DSA C

int scores[] = { [1] };

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

A10, 20, 30

B10 20 30

C"10, 20, 30"

D10; 20; 30

Attempts:

3 left

💡 Hint

Common Mistakes

Using spaces instead of commas between values.

Putting values inside quotes making it a string.

The array is initialized with three integer values separated by commas inside curly braces.

3fill in blank

hard

Fix the error in the array declaration to create an array 'data' of size 4.

DSA C

int data[[1]];

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

Afour

B0

C4

D-4

Attempts:

3 left

💡 Hint

Common Mistakes

Using a word instead of a number.

Using negative or zero size.

Array size must be a positive integer literal or constant. '4' is correct.

4fill in blank

hard

Fill both blanks to declare and initialize an array 'ages' with 3 elements: 18, 21, 25.

DSA C

int ages[[1]] = { [2] };

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

A3

B18, 21, 25

C18 21 25

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between size and number of values.

Using spaces instead of commas between values.

The array 'ages' has size 3 and is initialized with three values separated by commas.

5fill in blank

hard

Fill all three blanks to declare an array 'temps' of size 4 and initialize with 15, 20, 25, 30.

DSA C

int temps[[1]] = { [2] , [3] };

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

A4

B15, 20

C25, 30

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong size for the array.

Not separating all values with commas.

The array 'temps' has size 4 and is initialized with four values split into two parts separated by a comma.

Practice

1. 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;

C. int arr = 5;

D. int arr[5];

Solution

1. Step 1: Understand array declaration syntax in C

   In C, to declare an array of integers with size 5, the syntax is int arr[5];.

2. Step 2: Check each option

   int arr[5]; matches the correct syntax. Options A, B, and D are incorrect because they either miss the size, use wrong keywords, or assign a value instead of declaring an array.

3. Final Answer:

   int arr[5]; -> Option D

4. Quick Check:

   Array declaration = int arr[5]; [OK]

Hint: Array size goes inside square brackets after type [OK]

Common Mistakes:

• Forgetting to specify size inside brackets
• Using wrong keywords like 'array'
• Assigning a value instead of declaring

2. Which of the following is the correct way to initialize an integer array with values 1, 2, 3 in C?

easy

A. int arr[3] = (1, 2, 3);

B. int arr = {1, 2, 3};

C. int arr[3] = {1, 2, 3};

D. int arr[3] = [1, 2, 3];

Solution

1. Step 1: Recall array initialization syntax

   In C, arrays are initialized using curly braces with values inside, and size must be specified if not inferred.

2. Step 2: Evaluate each option

   int arr[3] = {1, 2, 3}; correctly declares an array of size 3 and initializes it with values 1, 2, 3. int arr = {1, 2, 3}; misses the size, C uses parentheses instead of braces, and D uses square brackets which is invalid.

3. Final Answer:

   int arr[3] = {1, 2, 3}; -> Option C

4. Quick Check:

   Array init uses braces and size = int arr[3] = {1, 2, 3}; [OK]

Hint: Use curly braces {} to initialize arrays with size [OK]

Common Mistakes:

• Using parentheses () instead of braces {}
• Omitting array size when required
• Using square brackets [] for initialization

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

int arr[4] = {10, 20};
for(int i = 0; i < 4; i++) {
    printf("%d ", arr[i]);
}

medium

A. 10 20 0 0

B. 10 20 0 20

C. 10 20 10 20

D. 10 20 garbage garbage

Solution

1. Step 1: Understand partial initialization of arrays

   When an array is partially initialized in C, the remaining elements are set to zero automatically.

2. Step 2: Trace the loop output

   arr[0] = 10, arr[1] = 20, arr[2] = 0, arr[3] = 0. The loop prints all four elements separated by spaces.

3. Final Answer:

   10 20 0 0 -> Option A

4. Quick Check:

   Partial init fills rest with 0 = 10 20 0 0 [OK]

Hint: Uninitialized array elements default to 0 if partially initialized [OK]

Common Mistakes:

• Assuming uninitialized elements have garbage values
• Confusing partial initialization with full initialization
• Miscounting array size in loop

4. Identify the error in the following C code snippet:

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

medium

A. Array size is not specified

B. Cannot assign values to array after declaration using braces

C. Missing semicolon after array declaration

D. Array elements must be initialized with parentheses

Solution

1. Step 1: Understand array assignment rules in C

   In C, arrays cannot be assigned values using braces after declaration. Initialization must happen at declaration.

2. Step 2: Check the code snippet

   The code tries to assign values to arr using braces after declaration, which is invalid syntax and causes a compilation error.

3. Final Answer:

   Cannot assign values to array after declaration using braces -> Option B

4. Quick Check:

   Array assignment after declaration with {} is invalid [OK]

Hint: Initialize arrays only at declaration with braces [OK]

Common Mistakes:

• Trying to assign arrays after declaration with {}
• Confusing initialization with assignment
• Using parentheses instead of braces

5. Given the following code, what will be the output?

int arr[] = {5, 10, 15};
int *ptr = arr;
for(int i = 0; i < 3; i++) {
    printf("%d ", *(ptr + i));
}

Choose the correct output.

hard

A. 5 10 15

B. 5 0 15

C. Garbage values

D. Compilation error

Solution

1. Step 1: Understand pointer and array relationship

   In C, the name of the array is a pointer to its first element. Pointer arithmetic allows accessing elements by offset.

2. Step 2: Trace the loop output

   Pointer ptr points to arr[0]. *(ptr + i) accesses arr[i]. Loop prints 5, 10, 15 separated by spaces.

3. Final Answer:

   5 10 15 -> Option A

4. Quick Check:

   Pointer arithmetic accesses array elements correctly = 5 10 15 [OK]

Hint: Array name acts as pointer to first element [OK]

Common Mistakes:

• Confusing pointer arithmetic syntax
• Assuming pointer points to garbage
• Forgetting array size in loop