One-dimensional arrays in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array element modification

What is the output of this C program?

C

#include <stdio.h>

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

A 3

B 5

C 6

D 9

💡 Hint

Remember array indexing starts at 0. arr[2] is changed to arr[0] + arr[4].

arr[0] is 1 and arr[4] is 5, so arr[2] becomes 1 + 5 = 6.

❓ Predict Output

intermediate

Sum of elements in an array

What is the output of this C program?

C

#include <stdio.h>

int main() {
    int nums[] = {10, 20, 30, 40};
    int sum = 0;
    for(int i = 0; i < 4; i++) {
        sum += nums[i];
    }
    printf("%d\n", sum);
    return 0;
}

A 40

B 100

C 90

D 10

💡 Hint

Add all elements: 10 + 20 + 30 + 40.

The sum is 10 + 20 + 30 + 40 = 100.

🔧 Debug

advanced

Identify the error in array access

What error will this C program produce when run?

C

#include <stdio.h>

int main() {
    int arr[3] = {1, 2, 3};
    printf("%d\n", arr[3]);
    return 0;
}

A Undefined behavior (out-of-bounds access)

B Compilation error: array index out of range

C Runtime error: segmentation fault

D Prints 0

💡 Hint

Array indices go from 0 to size-1. Accessing arr[3] is outside the array.

Accessing arr[3] is out of bounds and causes undefined behavior. The program may print garbage or crash, but no compile error occurs.

📝 Syntax

advanced

Which option causes a compilation error?

Which of the following array declarations will cause a compilation error in C?

A int arr[3] = {1, 2, 3, 4};

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

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

D int arr[5];

💡 Hint

Check if the initializer list fits the declared array size.

Option A tries to initialize an array of size 3 with 4 elements, which is a compilation error.

🚀 Application

expert

Find the number of elements in the array

What is the value of 'count' after running this C program?

C

#include <stdio.h>

int main() {
    int data[] = {5, 10, 15, 20, 25, 30};
    int count = sizeof(data) / sizeof(data[0]);
    printf("%d\n", count);
    return 0;
}

A 4

B 5

C 24

D 6

💡 Hint

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

The array has 6 elements. Dividing total size by element size gives 6.