Array Insertion at Beginning in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new element at the beginning of the array.

DSA C#

int[] arr = {1, 2, 3, 4};
int newElement = 0;
int[] newArr = new int[arr.Length + 1];
newArr[0] = [1];
for (int i = 0; i < arr.Length; i++) {
    newArr[i + 1] = arr[i];
}

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

Aarr.Length

Barr[0]

C0

DnewElement

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning arr[0] instead of the new element.

Using an index out of range.

Not increasing the array size.

To insert at the beginning, assign the new element to the first position of the new array.

2fill in blank

medium

Complete the code to shift elements right to make space at the beginning.

DSA C#

int[] arr = {5, 6, 7};
int[] newArr = new int[arr.Length + 1];
for (int i = arr.Length - 1; i >= 0; i--) {
    newArr[i + 1] = [1];
}

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

Aarr[i]

BnewArr[i]

Carr[i + 1]

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using newArr[i] instead of arr[i].

Using wrong index like i+1 on arr.

Looping in wrong direction.

We copy each element from the original array to the next index in the new array to shift right.

3fill in blank

hard

Fix the error in the code to correctly insert at the beginning.

DSA C#

int[] arr = {10, 20, 30};
int newElement = 5;
int[] newArr = new int[arr.Length + 1];
for (int i = 0; i < arr.Length; i++) {
    newArr[i + 1] = arr[i];
}
newArr[0] = [1];

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

Aarr[0]

BnewElement

Carr[arr.Length]

DnewArr[1]

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning arr[0] instead of newElement.

Using an invalid index like arr[arr.Length].

Assigning to newArr[1] instead of newArr[0].

The new element must be assigned to index 0 after the loop shifts elements.

4fill in blank

hard

Fill both blanks to create a new array with the element inserted at the beginning.

DSA C#

int[] arr = {3, 4, 5};
int newElement = 2;
int[] newArr = new int[arr.Length + 1];
newArr[[1]] = newElement;
for (int i = 0; i < arr.Length; i++) {
    newArr[[2]] = arr[i];
}

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

A0

Bi + 1

Ci

Darr.Length

Attempts:

3 left

💡 Hint

Common Mistakes

Putting new element at wrong index.

Not shifting elements correctly.

Using i instead of i+1 for newArr index.

The new element goes at index 0, and existing elements start from index 1 in the new array.

5fill in blank

hard

Fill all three blanks to insert a new element at the beginning and print the new array.

DSA C#

int[] arr = {7, 8, 9};
int newElement = 6;
int[] newArr = new int[arr.Length + 1];
newArr[[1]] = newElement;
for (int i = 0; i < arr.Length; i++) {
    newArr[[2]] = arr[i];
}
for (int i = 0; i < newArr.Length; i++) {
    Console.Write(newArr[[3]] + " ");
}

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

A0

Bi + 1

Ci

DnewElement

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong indices for insertion or shifting.

Printing newElement instead of array elements.

Off-by-one errors in loops.

Insert newElement at index 0, shift original elements starting at index 1, and print elements by index i.

Practice

1. What happens when you insert an element at the beginning of a fixed-size array in C#?

easy

A. The last element is removed and the new element is added at the start.

B. The new element replaces the first element without shifting others.

C. The array size automatically increases to fit the new element.

D. All existing elements shift one position to the right to make space.

Solution

1. Step 1: Understand fixed-size array behavior

   In C#, arrays have fixed size, so to insert at the beginning, elements must shift right.

2. Step 2: Effect of insertion at index 0

   The element at index 0 is replaced by the new element, and all others move one index higher.

3. Final Answer:

   All existing elements shift one position to the right to make space. -> Option D

4. Quick Check:

   Insert at start = shift right [OK]

Hint: Insert at start means shift all elements right [OK]

Common Mistakes:

• Thinking array size grows automatically
• Replacing first element without shifting
• Removing last element silently

2. Which of the following C# code snippets correctly inserts an integer 5 at the beginning of an array arr of size 5, shifting elements right?

easy

A. for (int i = arr.Length - 1; i > 0; i--) { arr[i] = arr[i - 1]; } arr[0] = 5;

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

C. arr[0] = 5; // No shifting needed

D. arr[arr.Length] = 5; // Add at end

Solution

1. Step 1: Identify correct loop for shifting right

   Loop must start from the end and move elements one step right to avoid overwriting.

2. Step 2: Assign new value at index 0

   After shifting, assign 5 to arr[0].

3. Final Answer:

   for (int i = arr.Length - 1; i > 0; i--) { arr[i] = arr[i - 1]; } arr[0] = 5; -> Option A

4. Quick Check:

   Shift right from end, then insert [OK]

Hint: Shift from end to start to avoid overwrite [OK]

Common Mistakes:

• Shifting left instead of right
• Assigning without shifting
• Using invalid index arr.Length

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

int[] arr = {10, 20, 30, 40, 50};
for (int i = arr.Length - 1; i > 0; i--) {
    arr[i] = arr[i - 1];
}
arr[0] = 5;
foreach (int num in arr) {
    Console.Write(num + " ");
}

medium

A. 5 10 20 30 50

B. 5 10 20 30 40

C. 5 20 30 40 50

D. 10 5 20 30 40

Solution

1. Step 1: Shift elements right

   Elements move right: arr[4]=arr[3]=40, arr[3]=arr[2]=30, arr[2]=arr[1]=20, arr[1]=arr[0]=10

2. Step 2: Insert 5 at index 0

   arr[0] = 5

3. Final Answer:

   5 10 20 30 40 -> Option B

4. Quick Check:

   Shift right + insert 5 at start = 5 10 20 30 40 [OK]

Hint: Trace shifts from end, then insert new value [OK]

Common Mistakes:

• Not shifting elements correctly
• Overwriting elements before shifting
• Incorrect final array print

4. The following code attempts to insert 99 at the beginning of an array arr but produces incorrect output. What is the error?

int[] arr = {1, 2, 3, 4, 5};
for (int i = 0; i < arr.Length - 1; i++) {
    arr[i + 1] = arr[i];
}
arr[0] = 99;

medium

A. The loop shifts elements left instead of right, overwriting data.

B. The assignment to arr[0] should be inside the loop.

C. The loop index range is incorrect; it should start from the end.

D. The array size is too small to insert a new element.

Solution

1. Step 1: Analyze loop direction and range

   The loop starts from 0 and moves forward, causing overwriting of elements.

2. Step 2: Correct loop should start from end

   To shift right safely, loop must start from last index and move backward.

3. Final Answer:

   The loop index range is incorrect; it should start from the end. -> Option C

4. Quick Check:

   Shift right requires backward loop [OK]

Hint: Shift right needs backward loop from end [OK]

Common Mistakes:

• Looping forward overwrites elements
• Assigning new value inside loop
• Ignoring fixed array size

5. You have an array arr = new int[6] {0, 1, 2, 3, 4, 5} and want to insert a new element 99 at the beginning without losing any data. Which approach correctly handles this?

hard

A. Create a new array of size 7, set arr2[0] = 99, then copy all elements of arr to arr2 starting at index 1.

B. Shift all elements right by one and assign 99 to arr[0], but last element is lost.

C. Replace arr[0] with 99 directly without shifting elements.

D. Use a List<int> instead of array to insert at beginning easily.

Solution

1. Step 1: Understand fixed array size limitation

   Original array size is 6, so inserting without losing data requires a bigger array.

2. Step 2: Create new larger array and copy elements

   Create new array size 7, assign 99 at index 0, then copy original elements starting at index 1.

3. Final Answer:

   Create a new array of size 7, set arr2[0] = 99, then copy all elements of arr to arr2 starting at index 1. -> Option A

4. Quick Check:

   New bigger array + copy elements = safe insertion [OK]

Hint: Use bigger array and copy to insert without loss [OK]

Common Mistakes:

• Trying to insert in fixed-size array losing last element
• Replacing without shifting
• Ignoring better data structures like List