Check if Stack is Empty or Full in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the stack is empty.

DSA C#

public bool IsEmpty() {
    return top [1] -1;
}

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

A!=

B<

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or < instead of == causes wrong empty check.

Using != will return true when stack is not empty.

The stack is empty when the top index is equal to -1.

2fill in blank

medium

Complete the code to check if the stack is full.

DSA C#

public bool IsFull() {
    return top [1] maxSize - 1;
}

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

A<

B==

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < or > instead of == causes wrong full check.

Using != will return true when stack is not full.

The stack is full when the top index equals maxSize - 1.

3fill in blank

hard

Fix the error in the condition to check if the stack is empty.

DSA C#

public bool IsEmpty() {
    return top [1] -1;
}

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

A==

B>=

C<=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Checking top == 0 instead of top == -1.

Using !=, >= or <= is incorrect for empty check.

The correct check for empty stack is top == -1. A common error is checking against 0 instead.

4fill in blank

hard

Fill both blanks to correctly check if the stack is full.

DSA C#

public bool IsFull() {
    return top [1] maxSize [2] 1;
}

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

A==

B+

C-

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '-' causes wrong index calculation.

Using '!=' instead of '==' causes wrong full check.

The stack is full when top equals maxSize minus 1, so use '==' and '-'.

5fill in blank

hard

Fill all three blanks to check if the stack is empty or full.

DSA C#

public bool IsEmptyOrFull() {
    return (top [1] -1) || (top [2] maxSize [3] 1);
}

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

A==

B!=

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes wrong checks.

Using '+' instead of '-' causes wrong full index.

The stack is empty if top == -1, and full if top == maxSize - 1.

Practice

1. What does the IsEmpty() method typically check in a stack data structure?

easy

A. If the stack has no elements inside

B. If the stack is full and cannot add more elements

C. If the stack has exactly one element

D. If the stack has more than one element

Solution

1. Step 1: Understand the purpose of IsEmpty()

   The IsEmpty() method checks whether the stack contains any elements or not.

2. Step 2: Interpret the meaning of empty stack

   An empty stack means it has zero elements inside, so no items to pop or peek.

3. Final Answer:

   If the stack has no elements inside -> Option A

4. Quick Check:

   IsEmpty() = true means stack is empty [OK]

Hint: Empty means zero elements inside the stack [OK]

Common Mistakes:

• Confusing empty with full
• Thinking IsEmpty checks for one element
• Assuming IsEmpty checks capacity

2. Which of the following is the correct C# syntax to check if a stack named myStack is full assuming it has a fixed size?

easy

A. if (myStack.Count == myStack.Capacity) { }

B. if (myStack.IsEmpty()) { }

C. if (myStack.Length == 0) { }

D. if (myStack.IsFull()) { }

Solution

1. Step 1: Understand stack properties in C#

   A stack with fixed size uses Count for current elements and Capacity for max size.

2. Step 2: Check if stack is full

   If Count equals Capacity, the stack is full and cannot add more elements.

3. Final Answer:

   if (myStack.Count == myStack.Capacity) { } -> Option A

4. Quick Check:

   Count == Capacity means full stack [OK]

Hint: Full means count equals capacity in fixed size stack [OK]

Common Mistakes:

• Using IsEmpty() to check full
• Checking Length property which stacks don't have
• Using IsFull() without defining it

3. Consider this C# code snippet:

Stack<int> stack = new Stack<int>(3);
stack.Push(10);
stack.Push(20);
stack.Push(30);
bool isFull = stack.Count == 3;
bool isEmpty = stack.Count == 0;
Console.WriteLine(isFull);
Console.WriteLine(isEmpty);

What will be the output?

medium

A. True\nTrue

B. True\nFalse

C. False\nTrue

D. False\nFalse

Solution

1. Step 1: Analyze stack operations

   Three elements (10, 20, 30) are pushed into a stack with capacity 3, so stack is full.

2. Step 2: Evaluate isFull and isEmpty values

   isFull = stack.Count == 3 is true; isEmpty = stack.Count == 0 is false.

3. Final Answer:

   True\nFalse -> Option B

4. Quick Check:

   Count=3 means full=true, empty=false [OK]

Hint: Count equals capacity means full; zero means empty [OK]

Common Mistakes:

• Assuming stack is empty after pushes
• Confusing isFull and isEmpty values
• Ignoring stack capacity

4. The following C# code tries to check if a stack is full but causes a compile error:

Stack<int> stack = new Stack<int>();
if (stack.IsFull()) {
    Console.WriteLine("Stack is full");
}

What is the error and how to fix it?

medium

A. Change Stack<int> to List<int>

B. Stack cannot be empty; remove the if condition

C. IsFull() method does not exist; use stack.Count == capacity instead

D. Use stack.IsEmpty() instead of IsFull()

Solution

1. Step 1: Identify the error

   The IsFull() method is not defined in C# Stack class, causing a compile error.

2. Step 2: Correct the check for full stack

   Use stack.Count == capacity to check if stack is full, since Stack has no IsFull() method.

3. Final Answer:

   IsFull() method does not exist; use stack.Count == capacity instead -> Option C

4. Quick Check:

   No IsFull() method in Stack class [OK]

Hint: Stack class has no IsFull(); check count vs capacity [OK]

Common Mistakes:

• Assuming IsFull() exists by default
• Using IsEmpty() to check full
• Changing data structure unnecessarily

5. You have a fixed size stack of capacity 5. After pushing 3 elements, you want to check if you can push 2 more without overflow. Which condition correctly checks this in C#?

hard

A. if (stack.Count - 2 >= 0) { /* safe to push */ }

B. if (stack.IsEmpty()) { /* safe to push */ }

C. if (stack.Count == 5) { /* safe to push */ }

D. if (stack.Count + 2 <= 5) { /* safe to push */ }

Solution

1. Step 1: Understand stack capacity and current count

   Stack capacity is 5, current count is 3, so 2 more pushes are possible if total does not exceed 5.

2. Step 2: Formulate condition to check safe push

   Check if current count plus 2 is less than or equal to capacity: stack.Count + 2 <= 5.

3. Final Answer:

   if (stack.Count + 2 <= 5) { /* safe to push */ } -> Option D

4. Quick Check:

   Count + pushes ≤ capacity means safe [OK]

Hint: Add pushes to count; compare with capacity [OK]

Common Mistakes:

• Using IsEmpty() to check push safety
• Checking count equals capacity incorrectly
• Subtracting pushes instead of adding