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

Challenge - 5 Problems

❓ Predict Output

intermediate

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

Consider the following C# code that deletes the first element from an array by shifting elements left. What will be printed?

DSA C#

int[] arr = {10, 20, 30, 40, 50};
int n = arr.Length;
for (int i = 1; i < n; i++) {
    arr[i - 1] = arr[i];
}
n--;
for (int i = 0; i < n; i++) {
    Console.Write(arr[i] + " ");
}

A 20 30 40 50

B 10 20 30 40 50

C 30 40 50

D 20 30 40 50 0

💡 Hint

Think about how elements are shifted and the new length after deletion.

The first element (10) is removed by shifting all elements left. The new array length is one less, so elements 20, 30, 40, 50 remain and are printed.

❓ Predict Output

intermediate

What happens if we delete the first element twice in a row?

Given the array and deletion code below, what will be the output after deleting the first element two times?

DSA C#

int[] arr = {5, 15, 25, 35, 45};
int n = arr.Length;
for (int d = 0; d < 2; d++) {
    for (int i = 1; i < n; i++) {
        arr[i - 1] = arr[i];
    }
    n--;
}
for (int i = 0; i < n; i++) {
    Console.Write(arr[i] + " ");
}

A 15 25 35 45

B 25 35 45

C 35 45

D 5 15 25 35 45

💡 Hint

Each deletion shifts elements left and reduces length by one.

First deletion removes 5, array becomes 15 25 35 45. Second deletion removes 15, array becomes 25 35 45.

🔧 Debug

advanced

Why does this code cause an error when deleting the first element?

Examine the code below. It attempts to delete the first element by shifting elements left. What error will it cause and why?

DSA C#

int[] arr = {1, 2, 3};
int n = arr.Length;
for (int i = 0; i < n; i++) {
    arr[i] = arr[i + 1];
}
n--;
for (int i = 0; i < n; i++) {
    Console.Write(arr[i] + " ");
}

A Compilation error due to invalid loop condition

B No error, output: 2 3

C NullReferenceException due to invalid array access

D IndexOutOfRangeException because arr[i + 1] accesses out of bounds

💡 Hint

Check the loop condition and array indexing carefully.

The loop runs from i=0 to i=n-1. At i=n-1, arr[i + 1] is arr[n], which is out of array bounds causing IndexOutOfRangeException.

🧠 Conceptual

advanced

What is the time complexity of deleting the first element from an array by shifting?

If you delete the first element of an array by shifting all other elements one position to the left, what is the time complexity in terms of n (array size)?

A O(n^2)

B O(1)

C O(n)

D O(log n)

💡 Hint

Consider how many elements need to be moved.

All elements except the first must be shifted left by one, so the operation takes time proportional to n.

🚀 Application

expert

After deleting the first element from an array, what is the state of the array?

Given the array arr = {7, 14, 21, 28} and code that deletes the first element by shifting left and reducing length by one, what is the printed output?

DSA C#

int[] arr = {7, 14, 21, 28};
int n = arr.Length;
for (int i = 1; i < n; i++) {
    arr[i - 1] = arr[i];
}
n--;
for (int i = 0; i < n; i++) {
    Console.Write(arr[i] + " -> ");
}
Console.Write("null");

A 14 -> 21 -> 28 -> null

B 7 -> 14 -> 21 -> 28 -> null

C 21 -> 28 -> null

D 14 -> 21 -> 28 -> 0 -> null

💡 Hint

Focus on how elements shift and the new length.

The first element 7 is removed by shifting left. The new length is 3, so elements 14, 21, 28 remain and are printed with arrows.

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