Array Access and Update at Index in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after updating an array element?

Consider the following C code that updates an element in an array. What will be the printed output?

DSA C

int arr[5] = {10, 20, 30, 40, 50};
arr[2] = 100;
for(int i = 0; i < 5; i++) {
    printf("%d ", arr[i]);
}

A 10 20 30 40 50

B 10 20 100 40 100

C 10 20 100 40 50

D 10 20 100 50 50

💡 Hint

Remember that array indices start at 0, so arr[2] is the third element.

The code changes the third element (index 2) from 30 to 100. The rest remain unchanged.

❓ Predict Output

intermediate

What happens when accessing an array out of bounds?

What is the output or behavior of this C code snippet?

DSA C

int arr[3] = {1, 2, 3};
printf("%d", arr[5]);

A Compilation error

B 0

C 3

D Undefined behavior (may print garbage or crash)

💡 Hint

Accessing outside the array size is not safe in C.

Accessing arr[5] goes beyond the allocated array size, causing undefined behavior.

🔧 Debug

advanced

Identify the error in updating array elements

What error will this C code produce when compiled or run?

DSA C

int arr[4] = {5, 10, 15, 20};
arr[4] = 25;
printf("%d", arr[4]);

A Undefined behavior at runtime

B Compilation error: array index out of bounds

C Runs and prints 25

D Runtime segmentation fault

💡 Hint

Array indices go from 0 to size-1.

The code compiles but accessing arr[4] is out of bounds causing undefined behavior.

❓ Predict Output

advanced

What is the final array after multiple updates?

Given the following code, what is the final printed array?

DSA C

int arr[5] = {1, 2, 3, 4, 5};
arr[0] = arr[4];
arr[4] = arr[1];
arr[1] = 10;
for(int i = 0; i < 5; i++) {
    printf("%d ", arr[i]);
}

A 5 10 3 4 2

B 1 10 3 4 2

C 5 2 3 4 10

D 5 1 3 4 10

💡 Hint

Track each assignment step by step.

arr[0] becomes 5 (old arr[4]), arr[4] becomes 2 (old arr[1]), arr[1] becomes 10.

🧠 Conceptual

expert

How many elements are in the array after this declaration?

What is the number of elements in this array in C?

DSA C

int arr[] = {7, 14, 21, 28, 35, 42};

A 5

B 6

C 7

D Undefined (needs explicit size)

💡 Hint

When size is omitted, the compiler counts the initializer elements.

The array has 6 elements because 6 values are given in the initializer.