add a multiplication operation

Add a member-function which performs multiplication of two float point
digits.

Signed-off-by: Sergii Piatakov <sergii.piatakov@globallogic.com>

calculator.cpp

@@ -9,3 +9,8 @@ int Calculator::Sub (double a, double b)
 {
     return Add (a, -b);
 }
+
+int Calculator::Mul (double a, double b)
+{
+    return a * b + 0.5;
+}

calculator.h

@@ -6,6 +6,7 @@ class Calculator
     public:
         int Add (double, double);
         int Sub (double, double);
+        int Mul (double, double);
 };
 
 #endif//CALCULATOR_H