refactoring: case(for mutiply and division)

src/main/c/Calculator/calculator.c

@@ -76,6 +76,10 @@ double combination(int n, int r);
             return num1 + num2;
         case 2:
             return num1 - num2;
+        case 3:
+            return num1 * num2;
+        case 4:
+            return num1 / num2;