diff --git a/src/conversionOfNumbers/conversionOfNumbers.h b/src/conversionOfNumbers/conversionOfNumbers.h
index 3422e06..b897a66 100644
--- a/src/conversionOfNumbers/conversionOfNumbers.h
+++ b/src/conversionOfNumbers/conversionOfNumbers.h
@@ -5,5 +5,6 @@ char* convertIntToBinaryStr(int input);
 int binaryStrLen(int input);
 unsigned int convertBinaryStrToInt(char* input);
 char* convertIntToHex(int input);
+int hexStrLen(int input);
 
 #endif
\ No newline at end of file