how to edit data stored in a MYSQL database through c ++

this is the code I have

system("cls");
   char sentencia[] = "SELECT * FROM c_alumnos WHERE Carnet=\'%s\'";
   MYSQL_RES *res;
   MYSQL_ROW  row; 

   std::cout<<"EDITAR DATO ALUMNO"<<std::endl;

   std::cout<<"Ingrese Carnet de Alumno"<<std::endl;
   std::cin>>alum.carnet;


   consulta = new char[strlen(sentencia)+strlen(alum.carnet)];   
   sprintf(consulta, sentencia, alum.carnet);
   res = mysql_store_result(ObjDatos);

   if(mysql_store_result(ObjDatos)>0)
   {
       row = mysql_fetch_row(res);
       sprintf(alum.carnet, "%s", row[0]);

       std::cout << "Ingrese direccion: ";
       std::cin >> alum.Direccion;  

       mysql_free_result(res);           
   }
   else
      std::cout << "Alumno no encontrado" <<std::endl;
 }