Correction of valid operation check

src/inputHandler.c

@@ -47,7 +47,7 @@ char getOperationSymbolById(int id) {
 
 // Checking if operation id is available
 int isOperationIdValid(int id) {
-    if(id < 0 || id > 7) return 0;
+    if(id < 1 || id > 7) return 0;
     return 1;
 }