📄 第五课 常 量 (常量是在程序运行过程中不能改变值的量，而变量是可以......) 第五课范例程序包.htm
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<TD class=TopLighNav1
height=22><font font> 第五课：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=黑体 font size="4">第五课 常量</FONT></DIV></TD></TR>
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<p style="line-height: 200%"><font font> 上一节我们学习了KEIL
C51编译器所支持的数据类型。而这些数据类型又是怎么用在常量和变量的定义中的呢？又有什么要注意的吗？下面就来看看吧。晕！你还区分不清楚什么是常量，什么是变量。常量是在程序运行过程中不能改变值的量，而变量是可以在程序运行过程中不断变化的量。变量的定义可以使用所有C51编译器支持的数据类型，而常量的数据类型只有整型、浮点型、字符型、字符串型和位标量。这一节我们学习常量定义和用法，而下一节则学习变量。<BR>常量的数据类型说明是这样的<BR> 1．
整型常量可以表示为十进制如123,0，－89等。十六进制则以0x开头如0x34,-0x3B等。长整型就在数字后面加字母L，如104L，034L，0xF340等。<BR> 2．
浮点型常量可分为十进制和指数表示形式。十进制由数字和小数点组成，如0.888,3345.345,0.0等，整数或小数部分为0，可以省略但必须有小数点。指数表示形式为[±]数字[.数字]e[±]数字，[]中的内容为可选项，其中内容根据具体情况可有可无，但其余部分必须有,如125e3,7e9,-3.0e-3。<BR> 3．
字符型常量是单引号内的字符，如'a','d'等，不可以显示的控制字符，可以在该字符前面加一个反斜杠"\"组成专用转义字符。常用转义字符表请看表5－1。<BR> 4．
字符串型常量由双引号内的字符组成，如"test","OK"等。当引号内的没有字符时，为空字符串。在使用特殊字符时同样要使用转义字符如双引号。在C中字符串常量是做为字符类型数组来处理的，在存储字符串时系统会在字符串尾部加上\o转义字符以作为该字符串的结束符。字符串常量"A"和字符常量'A'是不同的，前者在存储时多占用一个字节的字间。<BR> 5．
位标量，它的值是一个二进制。<BR></font></p>
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN
style="FONT-FAMILY: 宋体"><font font>转义字符<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: 宋体"><font font>含义<SPAN
lang=EN-US><O:P></O:P></SPAN></font></SPAN></P></TD>
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN lang=EN-US
style="FONT-FAMILY: 宋体"><font font>ASCII码（16/10进制）<O:P></O:P></font></SPAN></P></TD></TR>
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<P class=MsoNormal><SPAN lang=EN-US
style="FONT-FAMILY: 宋体"><font font>\o<O:P></O:P></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: 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: 宋体"><font font>空字符<SPAN
lang=EN-US>(NULL)<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: 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: 宋体"><font font>00H/0<O:P></O:P></font></SPAN></P></TD></TR>
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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: 宋体"><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"
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<P class=MsoNormal><SPAN style="FONT-FAMILY: 宋体"><font font>换行符<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: 宋体"><font font>0AH/10<O:P></O:P></font></SPAN></P></TD></TR>
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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: 宋体"><font font>\r<O:P></O:P></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: 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: 宋体"><font font>回车符<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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