Common array operations - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array sum calculation

What is the output of this C program that sums elements of an integer array?

C

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int sum = 0;
    for (int i = 0; i < 5; i++) {
        sum += arr[i];
    }
    printf("%d\n", sum);
    return 0;
}

A 10

B 15

C 5

D 0

💡 Hint

Add all numbers in the array: 1 + 2 + 3 + 4 + 5.

The loop adds each element of the array to sum. The total is 1+2+3+4+5 = 15.

❓ Predict Output

intermediate

Output of array element modification

What is the output of this C program that modifies elements of an array?

C

#include <stdio.h>

int main() {
    int arr[3] = {10, 20, 30};
    for (int i = 0; i < 3; i++) {
        arr[i] = arr[i] * 2;
    }
    for (int i = 0; i < 3; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 20 40 60

B 10 20 30

C 0 0 0

D 30 40 50

💡 Hint

Each element is multiplied by 2.

The loop doubles each element, so 10->20, 20->40, 30->60.

❓ Predict Output

advanced

Output of searching for an element in array

What is the output of this C program that searches for a value in an array?

C

#include <stdio.h>

int main() {
    int arr[] = {5, 10, 15, 20, 25};
    int target = 15;
    int found = 0;
    for (int i = 0; i < 5; i++) {
        if (arr[i] == target) {
            found = 1;
            break;
        }
    }
    if (found) {
        printf("Found\n");
    } else {
        printf("Not Found\n");
    }
    return 0;
}

A 0

B Not Found

C 15

D Found

💡 Hint

Check if 15 is in the array.

The program finds 15 in the array and prints "Found".

❓ Predict Output

advanced

Output of array reversal

What is the output of this C program that reverses an array and prints it?

C

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4};
    int n = 4;
    for (int i = 0; i < n / 2; i++) {
        int temp = arr[i];
        arr[i] = arr[n - 1 - i];
        arr[n - 1 - i] = temp;
    }
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 4 3 2 1

B 1 2 3 4

C 2 1 4 3

D 1 4 3 2

💡 Hint

The program swaps elements from start and end.

The array is reversed, so the output is "4 3 2 1 ".

🧠 Conceptual

expert

Number of elements in a statically declared array

Given the declaration int arr[10];, what is the value of sizeof(arr) / sizeof(arr[0]) in C?

A Depends on compiler

B 4

C 10

D 40

💡 Hint

sizeof(arr) gives total bytes, sizeof(arr[0]) gives bytes per element.

The expression calculates the number of elements by dividing total size by element size, which is 10.