Array Deletion at Beginning in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the first element from the array by shifting elements.

DSA C#

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

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

Ai + 1

Bi - 1

Ci

Darr.Length

Attempts:

3 left

💡 Hint

Common Mistakes

Using i - 1 causes index out of range at i=0.

Using i copies the same element, no shift happens.

We shift each element to the left by assigning arr[i] = arr[i + 1].

2fill in blank

medium

Complete the code to set the last element to zero after shifting.

DSA C#

arr[arr.Length [1] 1] = 0;

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

A/

B+

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using + 1 causes index out of range error.

Using * or / is not correct for indexing.

We use arr.Length - 1 to access the last element and set it to zero.

3fill in blank

hard

Fix the error in the loop condition to avoid index out of range.

DSA C#

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

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

Aarr.Length

Barr.Length - 1

Carr.Length + 1

Darr.Length / 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr.Length causes index out of range.

Using arr.Length + 1 is invalid and causes errors.

The loop must stop at arr.Length - 1 to avoid accessing beyond the array.

4fill in blank

hard

Fill both blanks to complete the method that deletes the first element from the array.

DSA C#

public static void DeleteFirst(int[] arr) {
    for (int i = 0; i < [1]; i++) {
        arr[i] = arr[i [2] 1];
    }
    arr[arr.Length - 1] = 0;
}

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

Aarr.Length - 1

Barr.Length

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr.Length causes index out of range.

Using - 1 inside the loop causes wrong shifting.

The loop runs till arr.Length - 1 and shifts elements left by using i + 1.

5fill in blank

hard

Fill all three blanks to create a method that deletes the first element and returns the new array length.

DSA C#

public static int DeleteFirstElement(int[] arr) {
    for (int i = 0; i < [1]; i++) {
        arr[i] = arr[i [2] 1];
    }
    arr[arr.Length [3] 1] = 0;
    return arr.Length - 1;
}

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

Aarr.Length - 1

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr.Length as loop limit causes errors.

Using - 1 inside the loop index causes wrong shifting.

The loop runs till arr.Length - 1, shifts elements using i + 1, and sets last element at arr.Length - 1 to zero.

Practice

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

easy

A. All elements shift one position to the left, and the last element becomes unused.

B. The array size decreases automatically by one.

C. The first element is replaced by null but others stay the same.

D. The array elements remain unchanged.

Solution

1. Step 1: Understand array fixed size in C#

   Arrays have fixed size; deleting an element does not reduce size automatically.

2. Step 2: Effect of deleting first element

   To delete the first element, all other elements shift left by one to fill the gap.

3. Final Answer:

   All elements shift one position to the left, and the last element becomes unused. -> Option A

4. Quick Check:

   Deleting first element shifts left [OK]

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

Common Mistakes:

• Thinking array size changes automatically
• Assuming elements stay in place
• Believing first element becomes null only

2. Which of the following is the correct syntax to delete the first element from an array named arr in C# by shifting elements?

easy

A. arr.RemoveAt(0);

B. for(int i = 0; i < arr.Length - 1; i++) arr[i] = arr[i + 1];

C. for(int i = 1; i < arr.Length; i++) arr[i] = arr[i - 1];

D. arr.Delete(0);

Solution

1. Step 1: Understand array element shifting

   To delete first element, shift elements left starting from index 0 to length-2.

2. Step 2: Check syntax correctness

   for(int i = 0; i < arr.Length - 1; i++) arr[i] = arr[i + 1]; correctly loops from 0 to length-2 and assigns arr[i] = arr[i+1].

3. Final Answer:

   for(int i = 0; i < arr.Length - 1; i++) arr[i] = arr[i + 1]; -> Option B

4. Quick Check:

   Loop from 0 to length-2 shifting elements left [OK]

Hint: Shift elements from index 0 to length-2 left [OK]

Common Mistakes:

• Starting loop from 1 instead of 0
• Using non-existent array methods like RemoveAt
• Assigning elements in wrong direction

3. What is the output of the following C# code?

int[] arr = {10, 20, 30, 40};
for(int i = 0; i < arr.Length - 1; i++) {
  arr[i] = arr[i + 1];
}
arr[arr.Length - 1] = 0;
for(int i = 0; i < arr.Length; i++) {
  Console.Write(arr[i] + " ");
}

medium

A. 20 30 40 0

B. 10 20 30 40

C. 0 20 30 40

D. 20 30 40 40

Solution

1. Step 1: Trace the shifting loop

   Loop shifts elements left: arr[0]=20, arr[1]=30, arr[2]=40.

2. Step 2: Set last element to 0

   arr[3] = 0 replaces old last element 40.

3. Final Answer:

   20 30 40 0 -> Option A

4. Quick Check:

   Shift left + last zero = 20 30 40 0 [OK]

Hint: Shift left then zero last element for deletion [OK]

Common Mistakes:

• Not setting last element to zero
• Confusing loop range causing wrong shifts
• Printing old array without changes

4. Identify the error in the following code that tries to delete the first element of an array arr and fix it:

int[] arr = {5, 10, 15, 20};
for(int i = 1; i < arr.Length; i++) {
  arr[i] = arr[i - 1];
}
arr[arr.Length - 1] = 0;

medium

A. Last element should not be set to zero.

B. Array size must be reduced before shifting.

C. Loop direction is wrong; should shift elements left, not right.

D. The loop should start from 0 and go to arr.Length - 2.

Solution

1. Step 1: Analyze loop direction

   The loop copies arr[i-1] to arr[i], shifting elements right, which is incorrect for deletion.

2. Step 2: Correct loop to shift elements left

   Loop should assign arr[i] = arr[i+1] starting from i=0 to length-2.

3. Final Answer:

   Loop direction is wrong; should shift elements left, not right. -> Option C

4. Quick Check:

   Shift left to delete first element [OK]

Hint: Shift elements left, not right, when deleting at start [OK]

Common Mistakes:

• Shifting elements in wrong direction
• Trying to reduce array size directly
• Ignoring last element cleanup

5. You have an array int[] arr = {3, 6, 9, 12, 15}. Write a method to delete the first element and return a new array with the remaining elements only (size reduced by one). Which approach is correct?

hard

A. Use arr.RemoveAt(0) to delete the first element.

B. Shift elements left in original array and keep the same size.

C. Set arr[0] = 0 and return the original array.

D. Create a new array of size arr.Length - 1 and copy elements from index 1 onward.

Solution

1. Step 1: Understand fixed size arrays

   Arrays in C# have fixed size; to reduce size, create a new array.

2. Step 2: Copy elements except first

   Create new array of size one less and copy elements from index 1 onward.

3. Final Answer:

   Create a new array of size arr.Length - 1 and copy elements from index 1 onward. -> Option D

4. Quick Check:

   New smaller array with elements from index 1 [OK]

Hint: Create new smaller array and copy from index 1 [OK]

Common Mistakes:

• Trying to resize original array directly
• Only shifting elements without resizing
• Using non-existent RemoveAt method on array