Heap-Free Polymorphic Driver

#include <iostream>
using namespace std;

class Driver {
public:
    virtual void startTransfer() = 0;
    virtual ~Driver() {}
};

class SpiDriver : public Driver {
public:
    void startTransfer() {
        cout << "SPI transfer started" << endl;
    }
};

class I2cDriver : public Driver {
public:
    void startTransfer() {
        cout << "I2C transfer started" << endl;
    }
};

int main() {
    int mode;
    cin >> mode;
    Driver* driver= nullptr; 
    SpiDriver spi;
    I2cDriver i2c;

    if(mode ==0)
    {
        driver = &spi;
    }
    else
    {
        driver = &i2c;
    }

    driver->startTransfer();
    // TODO:
    // Select the correct driver WITHOUT using dynamic allocation
    // Call startTransfer() polymorphically

    return 0;
}

Solving Approach