Merge remote-tracking branch 'upstream/master'

src/calc.cpp

@@ -32,6 +32,8 @@ int evaluate(const std::string &s) {
     case '/': change_stack_state(divide,   stack); break;
     case '%': change_stack_state(modulo,   stack); break;
     case '0'...'9': stack.push(c - '0'); break;
+    default:
+      throw std::invalid_argument( "received unrecognized character" );
     }
   }
 

src/main.cpp

@@ -10,6 +10,12 @@ int main() {
 
   std::cout << "User input is \"" << user_input << "\"\n";
 
-  const int result{evaluate(user_input)};
-  std::cout << "Result is: " << result << '\n';
+  try{
+    const int result{evaluate(user_input)};
+    std::cout << "Result is: " << result << '\n';
+  } catch (const std::invalid_argument& e){
+    std::cout << "encountered invalid argument" << e.what() << "\n";
+    return -1;
+  }
+
 }