Array initialization in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of partially initialized array

What is the output of this C program?

C

#include <stdio.h>

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

A 1 2 0 0 0

B 1 2 0 0 1

C 1 2 3 4 5

D 1 2 0 1 0

💡 Hint

Uninitialized elements in an array initialized with fewer values are set to zero.

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

❓ Predict Output

intermediate

Output of string array initialization

What will this C program print?

C

#include <stdio.h>

int main() {
    char str[6] = "Hello";
    for (int i = 0; i < 6; i++) {
        printf("%d ", str[i]);
    }
    return 0;
}

A 72 101 108 108 111 1

B 72 101 108 108 111 0

C 72 101 108 108 111 32

D 72 101 108 108 111 111

💡 Hint

Remember that strings in C end with a special null character.

The string "Hello" is stored as characters followed by a null terminator '\0' which has ASCII value 0.

❓ Predict Output

advanced

Output of multidimensional array initialization

What is the output of this C program?

C

#include <stdio.h>

int main() {
    int matrix[2][3] = {{1, 2}, {3}};
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }
    return 0;
}

A

1 2 0 
3 0 3 

B

1 2 3 
3 0 0 

C

1 2 0 
3 0 0 

D

1 2 0 
3 0 1 

💡 Hint

Uninitialized elements in nested arrays are set to zero.

In multidimensional arrays, missing elements in inner braces are set to zero, and missing inner braces initialize remaining elements to zero.

❓ Predict Output

advanced

Value of array element after initialization

What is the value of arr[3] after this code runs?

C

int arr[5] = {0, 1, 2, 3, 4};
arr[3] = arr[1] + arr[2];

A 4

B 1

C 2

D 3

💡 Hint

Look carefully at the assignment to arr[3].

arr[3] is assigned the sum of arr[1] (1) and arr[2] (2), so arr[3] becomes 3.

❓ Predict Output

expert

Output of array initialization with designated initializers

What is the output of this C program?

C

#include <stdio.h>

int main() {
    int arr[5] = {[2] = 10, [4] = 20};
    for (int i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 0 0 10 0 20

B 10 0 0 20 0

C 0 10 0 20 0

D 10 20 0 0 0

💡 Hint

Designated initializers set specific indexes; others default to zero.

Only arr[2] and arr[4] are set explicitly; others are zero by default.