词法分析

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这里是词法分析源程序代码：

#include <stdio.h>
#include <string.h>

char prog[80],token[8],ch;
int syn,p,m,n,sum;
char *rwtab[6]={"begin","if","then","while","do","end"};

void scaner(void);

main()
{
p=0;
printf("\n please input a string(end with ‘#‘):\n");

do{
scanf("%c",&ch);
prog[p++]=ch;
}while(ch!=‘#‘);

p=0;
do{
scaner();
switch(syn)
{
case 11:
printf("( %-10d%5d )\n",sum,syn);
break;

case -1:
printf("you have input a wrong string\n");
return 0;
break;
default:
printf("( %-10s%5d )\n",token,syn);
break;
}
}while(syn!=0);
}

void scaner(void)
{
sum=0;

for(m=0;m<8;m++)
{
token[m++]=NULL;
ch=prog[p++];
}
m=0;

while((ch==‘ ‘)||(ch==‘\n‘))
ch=prog[p++];

if(((ch<=‘z‘)&&(ch>=‘a‘))||((ch<=‘Z‘)&&(ch>=‘A‘)))
{
while(((ch<=‘z‘)&&(ch>=‘a‘))||((ch<=‘Z‘)&&(ch>=‘A‘))||((ch>=‘0‘)&&(ch<=‘9‘)))
{
token[m++]=ch;
ch=prog[p++];
}

p--;
syn=10;

for(n=0;n<6;n++)
if(strcmp(token,rwtab[n])==0)
{
syn=n+1;
break;
}
}
else if((ch>=‘0‘)&&(ch<=‘9‘))
{
while((ch>=‘0‘)&&(ch<=‘9‘))
{
sum=sum*10+ch-‘0‘;
ch=prog[p++];
}
p--;
syn=11;
}
else
{
switch(ch)
{
case ‘<‘:
token[m++]=ch;
ch=prog[p++];
if(ch==‘=‘)
{
syn=22;
token[m++]=ch;
}
else
{
syn=20;
p--;
}
break;

case ‘>‘:
token[m++]=ch;
ch=prog[p++];
if(ch==‘=‘)
{
syn=24;
token[m++]=ch;
}
else
{
syn=23;
p--;
}
break;

case ‘+‘:
token[m++]=ch;
ch=prog[p++];
if(ch==‘+‘)
{
syn=17;
token[m++]=ch;
}
else
{
syn=13;
p--;
}
break;

case ‘-‘:
token[m++]=ch;
ch=prog[p++];
if(ch==‘-‘)
{
syn=29;
token[m++]=ch;
}
else
{
syn=14;
p--;
}
break;

case ‘!‘:
ch=prog[p++];
if(ch==‘=‘)
{
syn=21;
token[m++]=ch;
}
else
{
syn=31;
p--;
}
break;

case ‘=‘:
token[m++]=ch;
ch=prog[p++];
if(ch==‘=‘)
{
syn=25;
token[m++]=ch;
}
else
{
syn=18;
p--;
}
break;

case ‘*‘:
syn=15;
token[m++]=ch;
break;

case ‘/‘:
syn=16;
token[m++]=ch;
break;

case ‘(‘:
syn=27;
token[m++]=ch;
break;

case ‘)‘:
syn=28;
token[m++]=ch;
break;

case ‘{‘:
syn=5;
token[m++]=ch;
break;

case ‘}‘:
syn=6;
token[m++]=ch;
break;

case ‘;‘:
syn=26;
token[m++]=ch;
break;

case ‘\"‘:
syn=30;
token[m++]=ch;
break;

case ‘#‘:
syn=0;
token[m++]=ch;
break;

case ‘:‘:
syn=17;
token[m++]=ch;
break;

default:
syn=-1;
break;
}
}
token[m++]=‘\0‘;
}

功能：这个程序是用来分析符号和字符的，对其目标进行输出，随后程序进行分析和输出。

对照表：图片不会加，请谅解

词法分析

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原文地址：http://www.cnblogs.com/zhichong/p/5924405.html