Array Deletion at Beginning in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to shift all elements left by one to delete the first element.

DSA C

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

Drag options to blanks, or click blank then click option'

Ai

Bi - 1

Ci + 1

Dn - i

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[i - 1] causes out-of-bound access at i=0.

Using arr[i] does not shift elements.

Using arr[n - i] accesses wrong indices.

To delete the first element, each element is replaced by the next element, so arr[i] = arr[i + 1].

2fill in blank

medium

Complete the code to reduce the array size after deletion.

DSA C

n = n [1] 1;

Drag options to blanks, or click blank then click option'

A+

B*

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using + increases the size incorrectly.

Using * or / changes size incorrectly.

After deleting the first element, the size of the array decreases by 1, so n = n - 1.

3fill in blank

hard

Fix the error in the loop condition to avoid out-of-bound access.

DSA C

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

Drag options to blanks, or click blank then click option'

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= n causes out-of-bound access.

Using > or >= is incorrect for forward loops.

The loop should run while i < n - 1 to avoid accessing arr[n], which is out of bounds.

4fill in blank

hard

Fill both blanks to complete the function that deletes the first element of the array.

DSA C

void deleteFirst(int arr[], int *n) {
    for(int i = 0; i [1] *n - 1; i++) {
        arr[i] = arr[i [2] 1];
    }
    (*n)--;
}

Drag options to blanks, or click blank then click option'

A<

B<=

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes out-of-bound access.

Using -1 instead of +1 accesses wrong elements.

The loop runs while i < *n - 1, and each element is replaced by the next element arr[i + 1].

5fill in blank

hard

Fill all three blanks to print the array after deleting the first element.

DSA C

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

Drag options to blanks, or click blank then click option'

A0

B<

C++

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 1 skips the new first element at index 0.

Using i-- or wrong loop condition causes errors.

After deletion, elements are shifted left and n is decremented, so the remaining elements are at indices 0 to n-1. Use i=0; i < n; i++.

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