％The phase locked loop(PLL),adjusts the phase of a local oscillator
％w.r.t the incoming modulated signal.In this way,the phase of the
％incoming signal is locked and the signal is demodulated.This scheme
％is used in PM and FM as well.
％We will implement it by using a closed loop system.Control systems
％techniques are applied here.
假定已經有許多應用采用了程序1 - 1 5中所定義的C u r r e n c y類，現在我們想要對C u r r e n c y類
的描述進行修改，使其應用頻率最高的兩個函數A d d和I n c r e m e n t可以運行得更快，從而提高應
用程序的執行速度。由于用戶僅能通過p u b l i c部分所提供的接口與C u r r e n c y類進行交互，
