by those i mean when i put " f " for saving the last output , the current output doesn't change . i understood it when i print " f " and " Tx " and that's why the counter doesn't increase .
and now the question is " why the output " Tx " doesn't change when i put " f " for saving last one in it and compare with current one " Tx" , while when i omit " f " from the code the current output start to change ?!?!"