fixing bugs, changing some code from char arrays to c++ std::string

src/client_backend/queue_ctrl.h

@@ -1,9 +1,9 @@
 #pragma once
 #ifndef QUEUE_CTRL_H
 #define QUEUE_CTRL_H
-
-int queue_push(char* str);
-int queue_pop(char* str);
+#include <string>
+int queue_push(const std::string& str);
+std::string queue_pop();
 int get_queue_size();
 
 #endif // !QUEUE_CTRL_H