Array Deletion at Beginning in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after deleting first element from array

What will be the output of the following C code after deleting the first element from the array?

DSA C

int arr[] = {10, 20, 30, 40, 50};
int n = 5;

// Delete first element by shifting
for (int i = 0; i < n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;

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

A 50 40 30 20

B 10 20 30 40 50

C 30 40 50

D 20 30 40 50

💡 Hint

After deleting the first element, all elements shift left by one position.

The code shifts all elements left by one, overwriting the first element. The size reduces by one, so the output prints elements from index 0 to n-1, which are 20, 30, 40, 50.

❓ Predict Output

intermediate

Resulting array size after deletion

Given an array of size 7, after deleting the first element by shifting, what is the new size of the array?

DSA C

int arr[7] = {5, 10, 15, 20, 25, 30, 35};
int n = 7;

// Delete first element
for (int i = 0; i < n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;

A 7

B 6

C 5

D 0

💡 Hint

Deleting one element reduces the size by one.

The size variable n is decremented by one after deletion, so new size is 6.

🔧 Debug

advanced

Identify the bug in array deletion code

What is the bug in the following code that deletes the first element of an array?

DSA C

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

for (int i = 0; i <= n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;

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

A Loop condition should be i < n - 1, not i <= n - 1

B n should be incremented, not decremented

C Array size is not initialized

D No bug, code works correctly

💡 Hint

Check the loop boundary to avoid accessing out of bounds.

The loop runs one step too far, accessing arr[n] which is out of bounds. It should run till i < n - 1 to avoid this.

❓ Predict Output

advanced

Output after multiple deletions at beginning

What is the output after deleting the first element twice from the array?

DSA C

int arr[] = {100, 200, 300, 400, 500};
int n = 5;

// Delete first element twice
for (int d = 0; d < 2; d++) {
    for (int i = 0; i < n - 1; i++) {
        arr[i] = arr[i + 1];
    }
    n--;
}

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

A 100 200 300 400 500

B 200 300 400 500

C 300 400 500

D 400 500

💡 Hint

Each deletion shifts elements left and reduces size by one.

After first deletion, array is 200,300,400,500; after second deletion, 300,400,500 remain.

🧠 Conceptual

expert

Time complexity of deleting first element in array

What is the time complexity of deleting the first element from an array of size n by shifting all elements left by one?

A O(n)

B O(1)

C O(n^2)

D O(log n)

💡 Hint

Consider how many elements need to be moved.

Deleting the first element requires shifting all remaining n-1 elements left, so time complexity is linear O(n).

Practice

1. What happens to the elements of an array when you delete the first element (at the beginning)?

easy

A. All elements shift one position to the right, and the last element is removed.

B. All elements shift one position to the left, and the first element is removed.

C. The array size increases by one.

D. The array remains unchanged.

Solution

1. Step 1: Understand deletion at beginning

   Deleting the first element means removing the element at index 0.

2. Step 2: Effect on remaining elements

   All other elements move one position left to fill the gap.

3. Final Answer:

   All elements shift one position to the left, and the first element is removed. -> Option B

4. Quick Check:

   Deletion at start shifts elements left [OK]

Hint: Deleting start shifts all elements left by one [OK]

Common Mistakes:

• Thinking elements shift right instead of left
• Assuming array size increases
• Believing array stays unchanged

2. Which of the following C code snippets correctly deletes the first element of an integer array arr of size n by shifting elements left?

easy

A. for(int i = 0; i < n; i++) { arr[i] = arr[i]; } n--;

B. for(int i = n - 1; i > 0; i--) { arr[i] = arr[i - 1]; } n++;

C. for(int i = 0; i < n - 1; i++) { arr[i] = arr[i + 1]; } n--;

D. for(int i = 1; i < n; i++) { arr[i] = arr[i - 1]; } n--;

Solution

1. Step 1: Identify correct loop for shifting left

   The loop must start from index 0 and assign arr[i] = arr[i+1] up to n-2.

2. Step 2: Check array size update

   After shifting, size decreases by 1 (n--).

3. Final Answer:

   for(int i = 0; i < n - 1; i++) { arr[i] = arr[i + 1]; } n--; -> Option C

4. Quick Check:

   Shift left from 0 to n-2, then reduce size [OK]

Hint: Shift elements left from 0 to n-2, then decrease size [OK]

Common Mistakes:

• Looping backwards instead of forwards
• Increasing size instead of decreasing
• Incorrect loop bounds causing overwrite

3. What is the output array after deleting the first element from int arr[] = {10, 20, 30, 40, 50}; using the correct deletion method?

medium

A. [50, 40, 30, 20]

B. [10, 20, 30, 40]

C. [30, 40, 50]

D. [20, 30, 40, 50]

Solution

1. Step 1: Remove first element 10

   Deleting first element removes 10 from the array.

2. Step 2: Shift remaining elements left

   Elements 20, 30, 40, 50 shift left to fill index 0 to 3.

3. Final Answer:

   [20, 30, 40, 50] -> Option D

4. Quick Check:

   First element removed, others shifted left [OK]

Hint: After deletion, array starts from second element [OK]

Common Mistakes:

• Leaving original first element in array
• Removing last element instead
• Reversing array order

4. Consider this code snippet for deleting the first element of an array:

for(int i = 1; i < n; i++) { arr[i-1] = arr[i]; } n--;

What is the error in this code?

medium

A. The loop correctly shifts elements; no error present.

B. The loop should start from i = 0, not 1.

C. The array size should be increased, not decreased.

D. The assignment should be arr[i] = arr[i-1], not arr[i-1] = arr[i].

Solution

1. Step 1: Analyze loop start and assignments

   The loop starts at i=1 and assigns arr[i-1] = arr[i], shifting elements left correctly.

2. Step 2: Check array size update

   Decreasing n by 1 after shifting is correct to reflect deletion.

3. Final Answer:

   The loop correctly shifts elements; no error present. -> Option A

4. Quick Check:

   Loop from 1 with arr[i-1]=arr[i] shifts left [OK]

Hint: Loop from 1 with arr[i-1]=arr[i] shifts left correctly [OK]

Common Mistakes:

• Thinking loop must start at 0 for shifting left
• Confusing assignment direction
• Incorrectly changing array size

5. You have an array int arr[] = {5, 10, 15, 20, 25, 30}; and size n = 6. You delete the first element twice using the correct deletion method. What is the resulting array and size?

hard

A. Array: [15, 20, 25, 30], Size: 4

B. Array: [10, 15, 20, 25, 30], Size: 5

C. Array: [5, 10, 15, 20], Size: 4

D. Array: [20, 25, 30], Size: 3

Solution

1. Step 1: First deletion removes 5

   After first deletion, array becomes [10, 15, 20, 25, 30], size 5.

2. Step 2: Second deletion removes 10

   After second deletion, array becomes [15, 20, 25, 30], size 4.

3. Final Answer:

   Array: [15, 20, 25, 30], Size: 4 -> Option A

4. Quick Check:

   Two deletions remove first two elements, size reduces by 2 [OK]

Hint: Each deletion removes first element and reduces size by one [OK]

Common Mistakes:

• Not updating size after each deletion
• Deleting wrong elements
• Confusing array indexes after shifts