Array Declaration and Initialization in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of partially initialized array

What is the output of the following C code snippet?

DSA C

int arr[5] = {1, 2};
for (int i = 0; i < 5; i++) {
    printf("%d ", arr[i]);
}

A 1 2 0 0 1

B 1 2 3 4 5

C 1 2 0 0 0

D 1 2 2 2 2

💡 Hint

Uninitialized elements in a partially initialized array are set to zero.

In C, when you initialize an array with fewer elements than its size, the remaining elements are set to zero.

So arr[0] = 1, arr[1] = 2, and arr[2], arr[3], arr[4] = 0.

❓ Predict Output

intermediate

Output of array initialization with explicit size and values

What is the output of this C code?

DSA C

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

A 5 10 15

B 5 10 15 0

C 0 0 0

D 15 10 5

💡 Hint

All elements are explicitly initialized.

The array has size 3 and all elements are initialized explicitly.

So the output prints 5, 10, and 15 in order.

❓ Predict Output

advanced

Output of array without explicit size but with initialization

What will be printed by this C code?

DSA C

int arr[] = {7, 8, 9, 10};
for (int i = 0; i < 4; i++) {
    printf("%d ", arr[i]);
}

A 7 8 9 10

B 7 8 9 10 0

C 0 0 0 0

D 10 9 8 7

💡 Hint

Array size is inferred from initializer list.

When size is omitted, the compiler sets the array size to the number of initializer elements.

So arr has size 4 with values 7,8,9,10.

❓ Predict Output

advanced

Output of multi-dimensional array initialization

What is the output of this C code snippet?

DSA C

int arr[2][3] = {{1, 2, 3}, {4}};
for (int i = 0; i < 2; i++) {
    for (int j = 0; j < 3; j++) {
        printf("%d ", arr[i][j]);
    }
}

A 1 2 3 4 5 6

B 1 2 3 4 0 0

C 1 2 3 4 4 4

D 1 2 3 0 0 0

💡 Hint

Uninitialized elements in inner arrays are zero.

The first row is fully initialized: 1, 2, 3.

The second row has only the first element initialized to 4; the rest are zero.

🧠 Conceptual

expert

Size of array with partial initialization and no explicit size

Consider the declaration:
int arr[] = {3, 6, 9};
What is the size of the array arr in memory?

A Depends on compiler

B 0

C Size must be explicitly specified

D 3

💡 Hint

When size is omitted, it is inferred from initializer list length.

The compiler counts the number of elements in the initializer list and sets the array size accordingly.

Here, 3 elements means size 3.