dynamic-array.cpp

/*
 * ============================================================================
 * Topic : Dynamic array ADT
 * Level : Data structures — arrays
 * ----------------------------------------------------------------------------
 * What you'll learn
 *   Allocate an int array with new after the user chooses capacity.
 *   Support append, insert-after, remove, find, update, and display.
 *   Shift elements carefully when inserting or removing in the middle.
 * ----------------------------------------------------------------------------
 * How to run
 *   • OnlineGDB: https://www.onlinegdb.com/online_c++_compiler
 *     Open this file on GitHub → copy → paste into OnlineGDB → C++ → Run
 *   • Codespaces (whole repo): https://codespaces.new/baheesa/cpp-practice?quickstart=1
 *   • Local: g++ -std=c++17 -Wall -o app "03-data-structures/dynamic-array.cpp" && ./app
 * ----------------------------------------------------------------------------
 * Example input
 *   1 create capacity 5 → 2 append 10 → 2 append 20 → 7 display → 0
 * Example output
 *   10 20
 *   (size 2 / 5)
 * ============================================================================
 */

#include <iostream>
using namespace std;

// Contiguous ADT: capacity is fixed after create(); size is how many slots are live.
class DynamicArray {
    int* data;
    int capacity;
    int size;
public:
    DynamicArray() : data(nullptr), capacity(0), size(0) {}
    ~DynamicArray() { delete[] data; }  // free heap block (safe on nullptr)

    void create() {
        delete[] data;  // replace any previous allocation
        cout << "Capacity: ";
        cin >> capacity;
        data = new int[capacity];
        size = 0;
        cout << "Created.\n";
    }

    void append() {
        if (!data) { cout << "Create first.\n"; return; }       // edge: no buffer yet
        if (size >= capacity) { cout << "Full.\n"; return; }    // edge: no room
        cout << "Value: ";
        cin >> data[size++];  // write at the next free index, then grow size
    }

    void insertAfter() {
        if (!data || size == 0) { cout << "Empty.\n"; return; }
        if (size >= capacity) { cout << "Full.\n"; return; }
        int key, val;
        cout << "Insert after value: "; cin >> key;
        cout << "New value: "; cin >> val;
        int idx = -1;
        for (int i = 0; i < size; i++)
            if (data[i] == key) { idx = i; break; }
        if (idx < 0) { cout << "Key not found.\n"; return; }
        // Shift right from the end so we do not overwrite unread values.
        for (int i = size; i > idx + 1; i--)
            data[i] = data[i - 1];
        data[idx + 1] = val;
        size++;
    }

    void removeValue() {
        int key; cout << "Remove value: "; cin >> key;
        int idx = -1;
        for (int i = 0; i < size; i++)
            if (data[i] == key) { idx = i; break; }
        if (idx < 0) { cout << "Not found.\n"; return; }
        // Shift left to close the gap; last slot becomes unused (size--).
        for (int i = idx; i < size - 1; i++)
            data[i] = data[i + 1];
        size--;
        cout << "Removed.\n";
    }

    void find() {
        int key; cout << "Find: "; cin >> key;
        for (int i = 0; i < size; i++)
            if (data[i] == key) {
                cout << "Found at index " << i << '\n';
                return;
            }
        cout << "Not found.\n";
    }

    void update() {
        int key, val;
        cout << "Old value: "; cin >> key;
        cout << "New value: "; cin >> val;
        for (int i = 0; i < size; i++)
            if (data[i] == key) { data[i] = val; cout << "Updated.\n"; return; }
        cout << "Not found.\n";
    }

    void display() const {
        if (size == 0) { cout << "(empty)\n"; return; }
        for (int i = 0; i < size; i++)
            cout << data[i] << ' ';
        cout << "\n(size " << size << " / " << capacity << ")\n";
    }

    void menu() {
        int c;
        do {
            cout << "\n1 Create  2 Append  3 Insert after  4 Remove\n"
                 << "5 Find  6 Update  7 Display  0 Exit\nChoice: ";
            cin >> c;
            switch (c) {
                case 1: create(); break;
                case 2: append(); break;
                case 3: insertAfter(); break;
                case 4: removeValue(); break;
                case 5: find(); break;
                case 6: update(); break;
                case 7: display(); break;
            }
        } while (c != 0);
    }
};

int main() {
    DynamicArray a;
    a.menu();
    return 0;
}