lab2 feat: add constant folding

inc/expression.hpp

@@ -186,17 +186,22 @@ public:
 
 	std::shared_ptr<std::string> to_math_str(void) const
 	{
+		char buffer[128] = {0};
+
 		switch (t)
 		{
 		case VAR:
 			return v.s;
 		case CONST:
 		{
-			char buffer[128] = {0};
 			return std::make_shared<std::string>((std::ostringstream() << v.d).str());
 		}
 		case OPERATOR:
 			return std::make_shared<std::string>(op_math_str());
+		case CV:
+			return std::make_shared<std::string>((std::ostringstream() << "t" << v.cv.i).str());
+		case NAT:
+			return std::make_shared<std::string>("");
 		default:
 			return std::make_shared<std::string>("Not a valid token!");
 		}