basic skeletons of update and delete added

lexer.h

@@ -21,6 +21,8 @@ enum class TokenType {
 	keyword_create,
 	keyword_table,
 	keyword_where,
+    keyword_delete,
+    keyword_update,
 	keyword_from,
 	keyword_insert,
 	keyword_into,
@@ -75,7 +77,8 @@ public:
 	TokenType prevTokenType();
 
     static bool isRelationalOperator(TokenType token_type);
-	static bool isLogicalOperator(TokenType token_type);
+    static bool isLogicalOperator(TokenType token_type);
+	static bool isArithmeticalOperator(TokenType token_type);
 
 private:
 	TokenType type(const std::string &token);