Here is the *complete working Turbo C++ code* for questions *3 to 8*, written in old-style C++ (iostream.h, conio.h) and 100% compatible with *Turbo C++ 3.0*.

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### ✅ *Q3. Volume Using Function Overloading*

cpp
#include <iostream.h>
#include <conio.h>

class VOLUME {
public:
    float findVolume(float side) {
        return side * side * side; // Cube
    }

    float findVolume(float l, float b, float h) {
        return l * b * h; // Box
    }

    float findVolume(double radius) {
        return (4.0 / 3) * 3.14 * radius * radius * radius; // Sphere
    }

    float findVolume(double radius, float height) {
        return 3.14 * radius * radius * height; // Cylinder
    }
};

void main() {
    clrscr();
    VOLUME v;

    cout << "Volume of Cube (side 5): " << v.findVolume(5.0f);
    cout << "\nVolume of Box (2x3x4): " << v.findVolume(2.0f, 3.0f, 4.0f);
    cout << "\nVolume of Sphere (radius 3): " << v.findVolume(3.0);
    cout << "\nVolume of Cylinder (radius 2, height 5): " << v.findVolume(2.0, 5.0f);

    getch();
}


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### ✅ *Q4. Area Using Constructor Overloading*

cpp
#include <iostream.h>
#include <conio.h>

class AREA {
public:
    AREA(int side) {
        cout << "Area of Square: " << side * side << "\n";
    }

    AREA(int l, int b) {
        cout << "Area of Rectangle: " << l * b << "\n";
    }

    AREA(float radius) {
        cout << "Area of Circle: " << 3.14 * radius * radius << "\n";
    }

    AREA(float base, float height, int dummy) {
        cout << "Area of Triangle: " << 0.5 * base * height << "\n";
    }
};

void main() {
    clrscr();
    AREA a1(4);                 // Square
    AREA a2(5, 6);              // Rectangle
    AREA a3(3.5f);              // Circle
    AREA a4(4.0f, 5.0f, 0);     // Triangle
    getch();
}


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### ✅ *Q5. Friend Function to Swap Price*

cpp
#include <iostream.h>
#include <conio.h>

class PRODUCT {
private:
    int pid;
    float price;

public:
    void input() {
        cout << "Enter PID and Price: ";
        cin >> pid >> price;
    }

    void display() {
        cout << "PID: " << pid << ", Price: " << price << "\n";
    }

    void doExchange(PRODUCT &p) {
        float temp = price;
        price = p.price;
        p.price = temp;
    }

    friend void doSwap(PRODUCT &a, PRODUCT &b);
};

void doSwap(PRODUCT &a, PRODUCT &b) {
    float temp = a.price;
    a.price = b.price;
    b.price = temp;
}

void main() {
    clrscr();
    PRODUCT P1, P2;

    P1.input();
    P2.input();

    cout << "\nBefore Exchange (Member Function):\n";
    P1.display();
    P2.display();

    P1.doExchange(P2);

    cout << "\nAfter Exchange (Member Function):\n";
    P1.display();
    P2.display();

    doSwap(P1, P2);

    cout << "\nAfter Swap (Friend Function):\n";
    P1.display();
    P2.display();

    getch();
}


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### ✅ *Q6. Friend Function Between Two Classes*

cpp
#include <iostream.h>
#include <conio.h>

class SY; // Forward declaration

class FY {
private:
    int marks;
public:
    void input() {
        cout << "Enter FY Marks: ";
        cin >> marks;
    }

    void display() {
        cout << "FY Marks: " << marks << "\n";
    }

    friend void exchange(FY &f, SY &s);
};

class SY {
private:
    int marks;
public:
    void input() {
        cout << "Enter SY Marks: ";
        cin >> marks;
    }

    void display() {
        cout << "SY Marks: " << marks << "\n";
    }

    friend void exchange(FY &f, SY &s);
};

void exchange(FY &f, SY &s) {
    int temp = f.marks;
    f.marks = s.marks;
    s.marks = temp;
}

void main() {
    clrscr();
    FY fy;
    SY sy;

    fy.input();
    sy.input();

    cout << "\nBefore Exchange:\n";
    fy.display();
    sy.display();

    exchange(fy, sy);

    cout << "\nAfter Exchange:\n";
    fy.display();
    sy.display();

    getch();
}


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### ✅ *Q7. Menu-Driven BILL Program*

cpp
#include <iostream.h>
#include <conio.h>

class BILL {
    int pid[5];
    int price[5];
    int count;

public:
    void initCount() {
        count = 0;
    }

    void takeProducts() {
        if (count < 5) {
            cout << "Enter PID: ";
            cin >> pid[count];
            cout << "Enter Price: ";
            cin >> price[count];
            count++;
        } else {
            cout << "Product limit reached!\n";
        }
    }

    void displayProducts() {
        for (int i = 0; i < count; i++) {
            cout << "PID: " << pid[i] << ", Price: " << price[i] << "\n";
        }
    }

    void displayTotalPrice() {
        int total = 0;
        for (int i = 0; i < count; i++) {
            total += price[i];
        }
        cout << "Total Bill: " << total << "\n";
    }
};

void main() {
    clrscr();
    BILL b;
    int choice;
    b.initCount();

    do {
        cout << "\n1. Add Product";
        cout << "\n2. Display Products";
        cout << "\n3. Display Total Price";
        cout << "\n4. Exit\n";
        cout << "Enter your choice: ";
        cin >> choice;

        switch (choice) {
        case 1:
            b.takeProducts();
            break;
        case 2:
            b.displayProducts();
            break;
        case 3:
            b.displayTotalPrice();
            break;
        case 4:
            break;
        default:
            cout << "Invalid choice!\n";
        }

    } while (choice != 4);

    getch();
}


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### ✅ *Q8. Array of STUDENT Objects*

cpp
#include <iostream.h>
#include <conio.h>

class STUDENT {
private:
    int rollno;
    char name[20];
    float percentage;

public:
    void input() {
        cout << "Enter Roll No: ";
        cin >> rollno;
        cout << "Enter Name: ";
        cin >> name;
        cout << "Enter Percentage: ";
        cin >> percentage;
    }

    void display() {
        cout << "Roll No: " << rollno << ", Name: " << name << ", Percentage: " << percentage << "\n";
    }
};

void main() {
    clrscr();
    STUDENT s[5];
    int i;

    for (i = 0; i < 5; i++) {
        cout << "\nEnter details of student " << (i + 1) << ":\n";
        s[i].input();
    }

    cout << "\n--- Student Details ---\n";
    for (i = 0; i < 5; i++) {
        s[i].display();
    }

    getch();
}


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Let me know if you want all these in a single file or with input validations!