In the if statement:
if (pitch <=90 && pitch => 15 && button_state =(HIGH))
if (pitch <=90 && pitch => 15 && button_state =(HIGH))
you assign a new value to button_state, which is illegal.
This should read if (pitch <=90 && pitch => 15 && button_state == HIGH):
if (pitch <=90 && pitch => 15 && button_state == HIGH)