How do I separate interface and implementation cleanly for financial apps?

    // Interface for financial calculations
    class IFinancialCalculator {
        public:
            virtual double calculateInterest(double principal, double rate, int time) = 0;
            virtual double calculateLoanEMI(double principal, double rate, int term) = 0;
            virtual ~IFinancialCalculator() {}
    };

    // Implementation of the financial calculator
    class FinancialCalculator : public IFinancialCalculator {
        public:
            double calculateInterest(double principal, double rate, int time) override {
                return principal * rate * time / 100;
            }

            double calculateLoanEMI(double principal, double rate, int term) override {
                double monthlyRate = rate / (12 * 100);
                return (principal * monthlyRate * pow(1 + monthlyRate, term)) / (pow(1 + monthlyRate, term) - 1);
            }
    };

    // Usage of the interface and implementation
    int main() {
        IFinancialCalculator* calculator = new FinancialCalculator();
        double interest = calculator->calculateInterest(1000, 5, 2);
        double emi = calculator->calculateLoanEMI(50000, 10, 60);
        
        delete calculator;
        return 0;
    }