diff --git a/QRCodeLibrary/Method.cpp b/QRCodeLibrary/Method.cpp
index b573028..22da80f 100644
--- a/QRCodeLibrary/Method.cpp
+++ b/QRCodeLibrary/Method.cpp
@@ -21,11 +21,6 @@ QRCodeMethod Method::determite_method(string input)
 	return type;
 }
 
-constexpr bool Method::is_num(char ch)
-{
-	return ch >= '0' && ch <= '9';
-}
-
 bool Method::is_alphabetic(char ch)
 {
 	return find(Tables::alphabetic.cbegin(), Tables::alphabetic.cend(), ch) != Tables::alphabetic.cend();
diff --git a/QRCodeLibrary/method.hpp b/QRCodeLibrary/method.hpp
index d3a7d5d..6e7a3a0 100644
--- a/QRCodeLibrary/method.hpp
+++ b/QRCodeLibrary/method.hpp
@@ -22,6 +22,6 @@ class Method {
 public:
 	static QRCodeMethod determite_method(string input);
 
-	static constexpr bool is_num(char ch);
+	static constexpr bool is_num(char ch) { return ch >= '0' && ch <= '9'; };
 	static bool is_alphabetic(char ch);
 };
\ No newline at end of file