fixed label position calculation

interpreter.cpp

@@ -34,7 +34,7 @@ std::string interpreter::eval(std::istream& in, bool& done) {
     // first pass: read program & resolve labels
     for (std::string line; std::getline(in, line); ++_pc) {
         if (line[0] == ':') {
-            _labels.emplace(line.substr(1), _pc);
+            _labels.emplace(line.substr(1), _pc--);
         } else {
             _prog.push_back(line);
         }