?? 第五課 常 量 (常量是在程序運行過程中不能改變值的量,而變量是可以......) 第五課范例程序包.htm
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<font color="#FF0000">單片機的c語言教程...由磁動力工作室明浩編寫.51單片機學習網(深圳學林電子有限公司)友情轉載</font>
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<TD class=TopLighNav1
height=22><font font> 第五課:常量</font></TD></TR></TBODY></TABLE></TH></TR></TBODY></TABLE></DIV></TD></TR></TBODY></TABLE></TD></TR>
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<DIV align=center><FONT face=黑體 font size="4">第五課 常量</FONT></DIV></TD></TR>
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<p style="line-height: 200%"><font font> 上一節我們學習了KEIL
C51編譯器所支持的數據類型。而這些數據類型又是怎么用在常量和變量的定義中的呢?又有什么要注意的嗎?下面就來看看吧。暈!你還區分不清楚什么是常量,什么是變量。常量是在程序運行過程中不能改變值的量,而變量是可以在程序運行過程中不斷變化的量。變量的定義可以使用所有C51編譯器支持的數據類型,而常量的數據類型只有整型、浮點型、字符型、字符串型和位標量。這一節我們學習常量定義和用法,而下一節則學習變量。<BR>常量的數據類型說明是這樣的<BR> 1.
整型常量可以表示為十進制如123,0,-89等。十六進制則以0x開頭如0x34,-0x3B等。長整型就在數字后面加字母L,如104L,034L,0xF340等。<BR> 2.
浮點型常量可分為十進制和指數表示形式。十進制由數字和小數點組成,如0.888,3345.345,0.0等,整數或小數部分為0,可以省略但必須有小數點。指數表示形式為[±]數字[.數字]e[±]數字,[]中的內容為可選項,其中內容根據具體情況可有可無,但其余部分必須有,如125e3,7e9,-3.0e-3。<BR> 3.
字符型常量是單引號內的字符,如'a','d'等,不可以顯示的控制字符,可以在該字符前面加一個反斜杠"\"組成專用轉義字符。常用轉義字符表請看表5-1。<BR> 4.
字符串型常量由雙引號內的字符組成,如"test","OK"等。當引號內的沒有字符時,為空字符串。在使用特殊字符時同樣要使用轉義字符如雙引號。在C中字符串常量是做為字符類型數組來處理的,在存儲字符串時系統會在字符串尾部加上\o轉義字符以作為該字符串的結束符。字符串常量"A"和字符常量'A'是不同的,前者在存儲時多占用一個字節的字間。<BR> 5.
位標量,它的值是一個二進制。<BR></font></p>
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN
style="FONT-FAMILY: 宋體"><font font>轉義字符<SPAN
lang=EN-US><O:P></O:P></SPAN></font></SPAN></P></TD>
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style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: windowtext 0.5pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt"
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN
style="FONT-FAMILY: 宋體"><font font>含義<SPAN
lang=EN-US><O:P></O:P></SPAN></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: windowtext 0.5pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt"
vAlign=top width=190>
<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>ASCII碼(16/10進制)<O:P></O:P></font></SPAN></P></TD></TR>
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vAlign=top width=189>
<P class=MsoNormal><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>\o<O:P></O:P></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
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<P class=MsoNormal><SPAN style="FONT-FAMILY: 宋體"><font font>空字符<SPAN
lang=EN-US>(NULL)<O:P></O:P></SPAN></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=190>
<P class=MsoNormal><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>00H/0<O:P></O:P></font></SPAN></P></TD></TR>
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<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext 0.5pt solid; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.1pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=189>
<P class=MsoNormal><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>\n<O:P></O:P></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=190>
<P class=MsoNormal><SPAN style="FONT-FAMILY: 宋體"><font font>換行符<SPAN
lang=EN-US>(LF)<O:P></O:P></SPAN></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=190>
<P class=MsoNormal><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>0AH/10<O:P></O:P></font></SPAN></P></TD></TR>
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<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: windowtext 0.5pt solid; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.1pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=189>
<P class=MsoNormal><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>\r<O:P></O:P></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=190>
<P class=MsoNormal><SPAN style="FONT-FAMILY: 宋體"><font font>回車符<SPAN
lang=EN-US>(CR)<O:P></O:P></SPAN></font></SPAN></P></TD>
<TD
style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 142.15pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
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<P class=MsoNormal><SPAN lang=EN-US
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