1. Pro.3.12

2. Currency
Exchange
App
Set exchange rate
Do exchange

3. Interface

4. Interface
SetExchangeRate(…)
DoExchange(…)

5. Currency
Exchange
Interface
SetExchangeRate(…)
DoExchange(…)

6. Currency
Exchange
Interface
SetExchangeRate(…)
DoExchange(…)
Test

7. Currency
Exchange
Interface
SetExchangeRate(…)
DoExchange(…)
Test

8. public interface ICurrencyExchange { void SetExchangeRate(…); double DoExchange(…); } public class CurrencyExchange : ICurrencyExchange //…

9. public interface ICurrencyExchange { void SetExchangeRate(…); double DoExchange(…); } public class CurrencyExchangeTest private ICurrencyExchange _currEx; //…