单片机c语言编程基础.doc

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1、优先级及预处理优先级问题表达式经常误认为的结果实际结果•的优先级高于*-＞操作符用于消除这个问题fp所指对象的字段f(*p).f对P取f偏移，作为指针，然后进行解除引用操作。*(p.f)[]高于*int*ap二ap是个指向int数组的指针int(*ap)ap是个元素为int指针的数组int*(ap[])函数()高于*int*fp()fp是个函数指针，所指函数返回intoint(*fp)0fp是个函数，返回int*int*(fp())==和!二高于位操作(val&mask!=0)(val&mask)!=0val&(ma

2、sk!=0)==和!二高于赋值符c=getchar()!=EOF(c=getchar())!=EOFc=(getchar()!=EOF)算术运算符高于位移运算符msb<<4+lsb(msb<<4)+lsbmsb<<(4+lsb)逗号运算符在所有运算符中优先级最低i=1,2i=(1,2)(i=1),2表(3.1)预处理指令预处理名称意义^define宏定义#undef撤销已定义过的宏名^include使编译程序将另一源文件嵌入到带有include的源文件中#if^if的一股令义是如果方「后面的衬量表达式为true.K编

3、泽它与-endifZ.间的代码.否则跳过这些代码.命令#endif标识个#if块的结束.-else命令的功能有点象C语肓中的else,丸Isc建立另一选择(在袴i「失败的情况下).衩li「命令意义与elseif同，它形成一个ifelse-if阶梯状语句，可进行多种编译选择.#else#elif#endif#ifdef用#ifdef与和'ndcl、金令分别表示“如果有定文“及“妇果无定文”・是条件编译的另一种方法。#ifndef#iine改变当前行数和文件名称.它们是在编泽程序中预先定义的标识符命令的基本形式如下：rr

4、linenumberf'filename"]terror编泽程序时.只要遇到terror就会生成一个编泽错误提示消息.并停止编译^pragma为实观时定义的命令.它允许向编泽程序传送务种指令例如.编译程序可能有一种选择.它又持对程序执疔的银踪.可用pragma语句指定一个报踪选择°另外ANSI标准C还定义了如下儿个宏：_LINE_表示正在编译的文件的行号_FILE_表示正在编译的文件的名字_DATE_表示编译时刻的I」期字符串，例如：“25Dec2007“_TIME_表示编译时刻的时间字符串,例如：”12:30:55

5、“_STDC_判断该文件是不是定义成标准C程序函数atoi与atof函数名：atoi功能：把字符串转换成长整型数JIJ彳去：intatoi(constchar*nptr);程序例：ixnixmiuuhxuxmiloxix"xuxmiaxxjuxjjxuixuiixjjxxjjuuixjxumumumi』』』』xuixuiixjjxuiuixxxmiumTTTTTTTTTTTTTTTTTrTTIITrTrTrTTTTTrTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTrrtrTrTTTfTT

6、TTTTTT~TTTTTTTTTTTTTTTTTT"xxTTTTTTTTTTTTTTTTTT~TT~TT~TTTTTTTTTTTTTlTrTTYrTTTrTrTTjTTrIttjTt11HHTT11itTfTtttItTfTr11Ittj11H7TTrTrTTTrTrTrTrTrTrTr11JITfTT11JiTfTTHf!TTr!TrTrTrTrTr7TffJfjt7TTrTrTTTrTrTrTrTrffJiITIfIT11HTTTf11TrTrTr#includeintmain(void){i

7、ntn;char*str=n12345.67H;n=atoi(str);printf(,fstring=%sinteger=%d*str,n);return0;}ixixulx』』xiixixuixxxmiuixixiiHixxxixumix11xxumiixuuaunixjxumixoiuuxxunnma1x11nixixuTTTTTTTTTT~TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTrrrrTTTTTTTTTTTTTTTTrrxrTTTTrr"TTTTTTTTTTTTrrxrTT

8、TTTTTTTrTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTrTTTrTTTrTTTTTTTTTT~TtTrTTTTTTff11TrTTttttttttttttttttttttTTTTTTTitTiTtTTTttttttttTtttttttttTttTTTTTTTTTTrTTTTTr7TtTtttTTTjTITttTTTrTT