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height=10><B><FONT color=#ffffff>首頁</FONT><FONT color=#ffffff>>
單片機教學(C語言教程)</FONT></B></TD>
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<DIV class=title1 align=center style4><B>第四課 數據類型</B> </DIV></TD></TR>
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<TD> 先來簡單說說C語言的標識符和關鍵字。標識符是用來標識源程序中某個對象的名字的,這些對象可以是語句、數據類型、函數、變量、數組等等。C語言是大小字敏感的一種高級語言,如果我們要定義一個定時器1,可以寫做"Timer1",如果程序中有"TIMER1",那么這兩個是完全不同定義的標識符。標識符由字符串,數字和下劃線等組成,注意的是第一個字符必須是字母或下劃線,如"1Timer"是錯誤的,編譯時便會有錯誤提示。有些編譯系統專用的標識符是以下劃線開頭,所以一般不要以下劃線開頭命名標識符。標識符在命名時應當簡單,含義清晰,這樣有助于閱讀理解程序。在C51編譯器中,只支持標識符的前32位為有效標識,一般情況下也足夠用了,除非你要寫天書:P。<BR> 關鍵字則是編程語言保留的特殊標識符,它們具有固定名稱和含義,在程序編寫中不允許標識符與關鍵資亦同。在KEIL
uVision2中的關鍵字除了有ANSI C標準的32個關鍵字外還根據51單片機的特點擴展了相關的關鍵字。其實在KEIL
uVision2的文本編輯器中編寫C程序,系統可以把保留字以不同顏色顯示,缺省顏色為天藍色。(<A
href="http://www.hificat.com/study/c%20lesson/addenda.htm"
target=_blank><FONT
color=#990000>標準和擴展關鍵字請看附錄一中的附表1-1和附表1-2</FONT></A>)<BR> 先看表4-1,表中列出了KEIL
uVision2
C51編譯器所支持的數據類型。在標準C語言中基本的數據類型為char,int,short,long,float和double,而在C51編譯器中int和short相同,float和double相同,這里就不列出說明了。下面來看看它們的具體定義:<BR></TD></TR>
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<P class=MsoNormal><SPAN style="FONT-FAMILY: 宋體">長 度<SPAN
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<P class=MsoNormal><SPAN style="FONT-FAMILY: 宋體">值 域<SPAN
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