diff --git a/src/main/c/taschenrechner.h b/src/main/c/taschenrechner.h
index 78ef6a1..6b7955b 100644
--- a/src/main/c/taschenrechner.h
+++ b/src/main/c/taschenrechner.h
@@ -85,5 +85,6 @@ double ConClock(double time, int startingUnit, int endingUnit);
 
 double ConTime(double time, int startingUnit, int endingUnit);
 
+int performOperation(int num1, char operator, int num2);
 
 #endif // TASCHENRECHNER_H