Check if Stack is Empty or Full in DSA C# - Build from Scratch

Check if Stack is Empty or Full

📖 Scenario: You are building a simple stack to manage plates in a kitchen. The stack can hold only a limited number of plates. You want to check if the stack is empty (no plates) or full (maximum plates) before adding or removing plates.

🎯 Goal: Create a stack with a fixed size, then write code to check if the stack is empty or full.

📋 What You'll Learn

Create an integer array called stack with size 5

Create an integer variable called top initialized to -1

Create an integer variable called maxSize set to 5

Write a condition to check if the stack is empty using top

Write a condition to check if the stack is full using top and maxSize

Print "Stack is empty" if empty

Print "Stack is full" if full

Print "Stack is neither empty nor full" otherwise

💡 Why This Matters

🌍 Real World

Stacks are used in many real-world applications like undo features in text editors, browser history, and managing function calls in programming.

💼 Career

Understanding stack operations and conditions is essential for software developers, especially when working with algorithms, memory management, and system design.

1

Create the stack data structure

Create an integer array called stack with size 5 and an integer variable called top initialized to -1.

DSA C#

int[] stack = new int[5];
int top = -1;
// Your code here

Hint

Use int[] stack = new int[5]; to create the stack array and int top = -1; to mark it empty.

2

Add the maximum size variable

Create an integer variable called maxSize and set it to 5.

DSA C#

int[] stack = new int[5];
int top = -1;
int maxSize = 5;
// Your code here

Hint

Use int maxSize = 5; to store the maximum stack size.

3

Check if the stack is empty or full

Write an if statement to check if the stack is empty by comparing top to -1, and an else if statement to check if the stack is full by comparing top to maxSize - 1.

DSA C#

int[] stack = new int[5];
int top = -1;
int maxSize = 5;

// Your code here

Hint

Use if (top == -1) to check empty and else if (top == maxSize - 1) to check full.

4

Print the stack state

Print "Stack is empty" if empty, "Stack is full" if full, and "Stack is neither empty nor full" otherwise using System.Console.WriteLine.

DSA C#

int[] stack = new int[5];
int top = -1;
int maxSize = 5;

if (top == -1)
{
    System.Console.WriteLine("Stack is empty");
}
else if (top == maxSize - 1)
{
    System.Console.WriteLine("Stack is full");
}
else
{
    System.Console.WriteLine("Stack is neither empty nor full");
}
// Your code here

Hint

Run the program to see the printed stack state.

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