Array Deletion at End in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to reduce the size of the array by one after deletion at the end.

DSA C

if (size > 0) {
    size [1] 1;
}

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

A-=

B+=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' instead of '-=' increases the size incorrectly.

Using '*=' or '/=' changes the size in unintended ways.

We use '-=' to decrease the size by one after deleting the last element.

2fill in blank

medium

Complete the code to check if the array is empty before deletion.

DSA C

if ([1] > 0) {
    size -= 1;
}

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

Acapacity

Blength

Cindex

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'capacity' instead of 'size' can cause errors because capacity is total space, not current elements.

Using 'index' or 'length' without proper context may cause logic errors.

We check if 'size' is greater than zero to ensure the array is not empty before deleting.

3fill in blank

hard

Fix the error in the code that deletes the last element from the array.

DSA C

if (size > 0) {
    array[size - 1] = 0; // Clear last element
    size [1] 1;
}

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

A+=

B=

C-=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' assigns a fixed value instead of decreasing size.

Using '+=' increases size incorrectly.

Using '*=' multiplies size, which is wrong here.

We must decrease 'size' by one using '-=' to reflect the deletion of the last element.

4fill in blank

hard

Fill both blanks to correctly delete the last element and update the size.

DSA C

if (size [1] 0) {
    array[size [2] 1] = 0;
    size -= 1;
}

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

A>

B-

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' in the condition causes wrong checks for empty array.

Using 'size' instead of 'size - 1' to access last element causes out-of-bounds error.

We check if size is greater than zero before deletion, and access the last element at index size - 1.

5fill in blank

hard

Fill all three blanks to delete the last element safely and update the array size.

DSA C

if (size [1] 0) {
    array[size [2] 1] = [3];
    size -= 1;
}

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

A>

B-

C0

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '-' for index causes out-of-bounds access.

Setting last element to a non-zero value does not clear it properly.

Checking size with '<' or '<=' causes wrong behavior.

We check if size is greater than zero, access last element at size - 1, and set it to 0 before decreasing size.

Practice

1. What happens to the size of an array when you delete an element from the end in a typical static array implementation?

easy

A. The size decreases by one

B. The size stays the same

C. The size increases by one

D. The size becomes zero

Solution

1. Step 1: Understand array size after deletion

   Deleting an element from the end means removing the last element, so the total number of elements reduces by one.

2. Step 2: Effect on array size

   The size variable or count of elements decreases by one to reflect the removal.

3. Final Answer:

   The size decreases by one -> Option A

4. Quick Check:

   Deleting last element reduces size by 1 [OK]

Hint: Deleting end element reduces size by one [OK]

Common Mistakes:

• Thinking size stays same after deletion
• Assuming size increases after deletion
• Confusing deletion with insertion

2. Which of the following is the correct way to delete the last element from an array arr of size n in C?

easy

A. free(arr[n-1]);

B. arr[n] = 0;

C. n = n - 1;

D. arr = arr - 1;

Solution

1. Step 1: Understand array deletion in C

   In static arrays, deleting means reducing the size count. So, decreasing n by 1 removes last element logically.

2. Step 2: Analyze options

   n = n - 1; correctly reduces size. arr[n] = 0; tries to set element but doesn't change size. free(arr[n-1]); is invalid as free is for dynamic memory. arr = arr - 1; is invalid pointer arithmetic.

3. Final Answer:

   n = n - 1; -> Option C

4. Quick Check:

   Decrease size variable to delete last element [OK]

Hint: Reduce size variable to delete last element [OK]

Common Mistakes:

• Using free() on static array elements
• Trying to set last element to zero without changing size
• Incorrect pointer arithmetic

3. What will be the output of the following C code?

int arr[5] = {10, 20, 30, 40, 50};
int n = 5;
n = n - 1;
for(int i = 0; i < n; i++) {
    printf("%d ", arr[i]);
}

medium

A. 10 20 30 40 50

B. 10 20 30 40

C. 20 30 40 50

D. 10 20 30

Solution

1. Step 1: Understand size after deletion

   Initially, n is 5. After n = n - 1;, n becomes 4, so loop runs from 0 to 3.

2. Step 2: Loop prints elements from index 0 to 3

   Elements printed are arr[0]=10, arr[1]=20, arr[2]=30, arr[3]=40.

3. Final Answer:

   10 20 30 40 -> Option B

4. Quick Check:

   Loop runs n=4 times, prints first 4 elements [OK]

Hint: After reducing size, loop prints fewer elements [OK]

Common Mistakes:

• Printing all 5 elements ignoring updated size
• Starting loop from 1 instead of 0
• Confusing array indices

4. Identify the error in the following code snippet that attempts to delete the last element of an array arr of size n.

void deleteEnd(int arr[], int n) {
    arr[n] = 0;
    n = n - 1;
}

medium

A. Accessing arr[n] is out of bounds

B. Size variable n should not be changed

C. Setting arr[n] to 0 deletes the element

D. Function should return the new size

Solution

1. Step 1: Check array index usage

   Array indices go from 0 to n-1. Accessing arr[n] is out of bounds and causes undefined behavior.

2. Step 2: Understand deletion logic

   To delete last element, reduce size n by 1. Setting arr[n] to 0 is invalid and does not delete element.

3. Final Answer:

   Accessing arr[n] is out of bounds -> Option A

4. Quick Check:

   Array index must be less than size [OK]

Hint: Array last index is n-1, not n [OK]

Common Mistakes:

• Using arr[n] instead of arr[n-1]
• Assuming setting element to zero deletes it
• Not updating size correctly

5. Given a dynamic array implemented with a pointer int *arr and current size n, which of the following correctly deletes the last element and updates the array size safely in C?

hard

A. free(arr[n-1]); n = n - 1;

B. arr[n-1] = 0; n = n - 1;

C. arr = arr - 1; n = n - 1;

D. n = n - 1; arr = realloc(arr, n * sizeof(int));

Solution

1. Step 1: Understand dynamic array deletion

   To delete last element, reduce size n by 1 and resize memory using realloc to avoid wasted space.

2. Step 2: Analyze options

   n = n - 1; arr = realloc(arr, n * sizeof(int)); correctly reduces size and resizes memory. arr[n-1] = 0; n = n - 1; sets element to zero but wastes memory. free(arr[n-1]); n = n - 1; incorrectly uses free on element. arr = arr - 1; n = n - 1; does invalid pointer arithmetic.

3. Final Answer:

   n = n - 1; arr = realloc(arr, n * sizeof(int)); -> Option D

4. Quick Check:

   Reduce size and resize memory with realloc [OK]

Hint: Use realloc after reducing size for dynamic arrays [OK]

Common Mistakes:

• Not resizing memory after deletion
• Using free() on array elements
• Incorrect pointer arithmetic