C++ Stack Exercises: Middle element of a stack (using a dynamic array)

Last update on April 14 2025 12:44:38 (UTC/GMT +8 hours)

23. Find the Middle Element of a Dynamic Array-Based Stack

Write a C++ program to find the middle element of a stack (using a dynamic array).

Test Data:
Input the size of the stack: 8
Input some elements onto the stack:
Stack elements are: 4 7 5 3 1
Reverse the said stack elements:
Stack elements are: 1 3 5 7 4

Sample Solution:

C++ Code:

#include <iostream>

using namespace std;

// Class representing a Stack
class Stack {
private:
    int* arra;     // Dynamic array to store elements
    int top;        // Index of top element
    int capacity;   // Maximum size of the stack

public:
    // Constructor to initialize the stack with a given size
    Stack(int size) {
        arra = new int[size]; // Allocate memory for the stack array
        top = -1;             // Initialize top index to -1 (empty stack)
        capacity = size;      // Set the maximum capacity of the stack
    }

    // Function to push an element onto the stack
    bool push(int x) {
        if (isFull()) {
            cout << "Stack overflow" << endl; // Display overflow message if the stack is full
            return false;
        }
        // Add element to array by incrementing top index
        arra[++top] = x;
        return true;
    }

    // Function to pop an element from the stack
    int pop() {
        if (isEmpty()) {
            cout << "Stack underflow" << endl; // Display underflow message if the stack is empty
            return 0;
        }
        // Return the top element and decrement the index of the top element
        return arra[top--];
    }

    // Function to peek the top element of the stack without removing it
    int peek() {
        if (isEmpty()) {
            cout << "Stack is empty" << endl; // Display message if the stack is empty
            return 0;
        }
        // Return the top element without modifying the top index
        return arra[top];
    }

    // Function to check if the stack is empty
    bool isEmpty() {
        // Stack is empty if top index is -1
        return (top < 0);
    }

    // Function to check if the stack is full
    bool isFull() {
        // Stack is full if top index is equal to capacity - 1
        return (top >= capacity - 1);
    }

    // Function to display the elements of the stack
    void display() {
        if (top < 0) {
            cout << "Stack is empty" << endl; // Display message if the stack is empty
            return;
        }
        cout << "\nStack elements are: ";
        for (int i = top; i >= 0; i--)
            cout << arra[i] << " "; // Display the elements of the stack
        cout << endl;
    }
};

// Function to find the middle element of the stack
int get_middle(Stack stk) {
    int length = 0;
    // Create a copy of the original stack
    Stack temp(stk);  
    while (!temp.isEmpty()) {
        length++;
        temp.pop();
    }
    int mid = length / 2;
    for (int i = 0; i < mid; i++) {
        // Remove elements before the middle element
        stk.pop();  
    }
    // Get the middle element
    int middle_element = stk.pop();  
    for (int i = mid; i < length - 1; i++) {
        // Restore the original stack
        stk.push(stk.pop());  
    }
    return middle_element;
}

int main() {
    int size;
    cout << "Input the size of the stack: ";
    cin >> size;
    Stack stk(size);
    cout << "\nInput some elements onto the stack:";
    stk.push(1);
    stk.push(3);
    stk.push(5);
    stk.push(7);
    stk.push(9);
    stk.push(10);
    stk.push(11);
    stk.display();
    int z = get_middle(stk); // Get the middle element of the stack
    cout << "Middle element = " << z;
    cout << "\n\nRemove one element from the said stack:";
    stk.pop();
    stk.display();
    z = get_middle(stk); // Get the middle element after removing one element
    cout << "\nMiddle element = " << z;
    return 0;
}

Sample Output:

Input the size of the stack: 8

Input some elements onto the stack:
Stack elements are: 11 10 9 7 5 3 1
Middle element = 7

Remove one element from the said stack:
Stack elements are: 10 9 7 5 3 1

Middle element = 5

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to determine the middle element in a dynamic array-based stack without modifying the stack.
• Develop a C++ program that computes the middle index of a dynamic stack and displays the corresponding element.
• Design a C++ program to implement a dynamic array-based stack and retrieve its middle element for both odd and even sizes.
• Implement a C++ program to access the middle element in a dynamic stack and verify the result with sample test cases.

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Previous C++ Exercise: Reverse a stack (using a dynamic array) elements.
Next C++ Exercise: Implement a stack using a vector with push, pop operations.