Array Deletion at End in DSA C - Execution Trace

Concept Flow - Array Deletion at End

Start with array

↓

Check if array is empty?

Yes→Stop: Nothing to delete

No↓

Remove last element

↓

Update array size

↓

Done

This flow shows checking if the array is empty, then removing the last element and updating the size.

Execution Sample

DSA C

int arr[5] = {10, 20, 30, 40, 50};
int size = 5;
// Delete last element
if (size > 0) {
  size--;
}

This code deletes the last element by reducing the size count if the array is not empty.

Execution Table

Step	Operation	Array Size	Pointer Changes	Visual State
1	Start with array	5	head -> arr[0]	[10, 20, 30, 40, 50]
2	Check if array is empty (size=5)	5	head -> arr[0]	[10, 20, 30, 40, 50]
3	Delete last element (size--)	4	head -> arr[0]	[10, 20, 30, 40, 50]
4	Done	4	head -> arr[0]	[10, 20, 30, 40, 50]

💡 Array size reduced from 5 to 4, last element logically removed

Variable Tracker

Variable	Start	After Step 3	Final
size	5	4	4
arr	[10, 20, 30, 40, 50]	[10, 20, 30, 40, 50]	[10, 20, 30, 40, 50]

Key Moments - 2 Insights

Why does the array still show the last element after deletion?

The execution_table row 3 shows size reduces to 4 but the array data remains unchanged. The last element is logically removed by ignoring it via size, not physically erased.

What happens if we try to delete when the array is empty?

Step 2 checks if size > 0. If size is 0, deletion stops immediately to avoid errors, as shown in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table at Step 3, what is the array size?

A 4

B 5

C 3

D 0

💡 Hint

Check the 'Array Size' column at Step 3 in execution_table

At which step does the array size change?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for 'Delete last element' operation in execution_table

If size was 0 at Step 2, what would happen next?

A Delete last element and reduce size

B Stop deletion, no change

C Array size becomes negative

D Array elements shift left

💡 Hint

Refer to concept_flow decision at 'Check if array is empty?'

Concept Snapshot

Array Deletion at End:
- Check if array size > 0
- Reduce size by 1 to delete last element
- Data remains but ignored beyond size
- No physical element removal
- Prevent deletion if empty

Full Transcript

We start with an array of size 5 containing elements 10, 20, 30, 40, 50. First, we check if the array is empty by verifying if size is greater than zero. Since size is 5, we proceed to delete the last element by reducing the size to 4. The array data remains unchanged, but logically the last element is removed by ignoring it beyond the new size. If the array was empty (size 0), deletion would stop immediately to avoid errors. This method efficiently deletes the last element by adjusting size without shifting or erasing data.

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