diff --git a/Operation.h b/Operation.h
index efe6ccd..a389718 100644
--- a/Operation.h
+++ b/Operation.h
@@ -1,3 +1,5 @@
+#pragma once
+
 enum class OpType
 {
     Addition, Subtraction, Multiplication, Division, Modulo, Special
diff --git a/basecalc.h b/basecalc.h
index a802ada..a357747 100644
--- a/basecalc.h
+++ b/basecalc.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "Operation.h"
 class BaseCalculator
 {
diff --git a/command.h b/command.h
index a836c75..961803a 100644
--- a/command.h
+++ b/command.h
@@ -1,3 +1,5 @@
+#pragma once
+
 class Command
 {
     public:
diff --git a/input_resolver.h b/input_resolver.h
index 3bbbbce..7368364 100644
--- a/input_resolver.h
+++ b/input_resolver.h
@@ -1,2 +1,4 @@
+#pragma once
+
 #include "command.h"
 Command resolveCommand();
\ No newline at end of file
diff --git a/special_calculator.h b/special_calculator.h
index 4bedb15..8ec22e2 100644
--- a/special_calculator.h
+++ b/special_calculator.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "basecalc.h"
 
 class SpecialCalculator: public BaseCalculator