diff --git a/interpreter.cpp b/interpreter.cpp
index 8f3a954..1543d6e 100644
--- a/interpreter.cpp
+++ b/interpreter.cpp
@@ -9,6 +9,7 @@
 #include "interpreter.hpp"
 #include <cctype>
 #include <algorithm>
+#include <iostream>
 
 int to_int(const std::string& val) {
     std::istringstream iss {val};
@@ -120,6 +121,7 @@ void interpreter::exec_instruction(const std::string& code, bool& done) {
     else if (code == "fun") fun();
     else if (code == "ret") ret();
     else if (code == "enl") enl();
+    else if (code == "out") out(); // for debugging
     else throw syntax_error {code};
 }
 
@@ -318,9 +320,9 @@ void interpreter::gne() {
 void interpreter::glt() {
     std::string label {_stack.back()};
     _stack.pop_back();
-    std::string val2 {_stack.back()};
+    int val2 {to_int(_stack.back())};
     _stack.pop_back();
-    std::string val1 {_stack.back()};
+    int val1 {to_int(_stack.back())};
     _stack.pop_back();
     if (val1 < val2) {
         _pc = _labels[label];
@@ -332,9 +334,9 @@ void interpreter::glt() {
 void interpreter::gle() {
     std::string label {_stack.back()};
     _stack.pop_back();
-    std::string val2 {_stack.back()};
+    int val2 {to_int(_stack.back())};
     _stack.pop_back();
-    std::string val1 {_stack.back()};
+    int val1 {to_int(_stack.back())};
     _stack.pop_back();
     if (val1 <= val2) {
         _pc = _labels[label];
@@ -346,9 +348,9 @@ void interpreter::gle() {
 void interpreter::ggt() {
     std::string label {_stack.back()};
     _stack.pop_back();
-    std::string val2 {_stack.back()};
+    int val2 {to_int(_stack.back())};
     _stack.pop_back();
-    std::string val1 {_stack.back()};
+    int val1 {to_int(_stack.back())};
     _stack.pop_back();
     if (val1 > val2) {
         _pc = _labels[label];
@@ -360,9 +362,9 @@ void interpreter::ggt() {
 void interpreter::gge() {
     std::string label {_stack.back()};
     _stack.pop_back();
-    std::string val2 {_stack.back()};
+    int val2 {to_int(_stack.back())};
     _stack.pop_back();
-    std::string val1 {_stack.back()};
+    int val1 {to_int(_stack.back())};
     _stack.pop_back();
     if (val1 >= val2) {
         _pc = _labels[label];
@@ -382,3 +384,10 @@ void interpreter::ret() {
     _pc = _calls.back();
     _calls.pop_back();
 }
+
+// debugging --------------------------------------------------------------
+
+void interpreter::out() {
+    std::cout << _stack.back() << '\n';
+    _pc++;
+}
diff --git a/interpreter.hpp b/interpreter.hpp
index 091a1a5..d042f03 100644
--- a/interpreter.hpp
+++ b/interpreter.hpp
@@ -71,6 +71,9 @@ class interpreter {
         // subroutines
         void fun();
         void ret();
+
+        // debugging
+        void out();
 };
 
 #endif // _interpreter_H_