词法分析

#include <stdio.h>
#include <string.h>
#include <conio.h>
#include <ctype.h>
void cffx();
char prog[80]={'\0'},
token[8];
char ch;
int syn,n,sum,m,p;
char *rwtab[6]={"begin","if","then","while","do","end"};
main()
{
p=0;
printf("\nplease input string:\n");
do {
ch=getchar();
prog[p++]=ch;
}while(ch!='#');

p=0;
do{
cffx();
switch(syn){
case 11: printf("(%d,%d)\n",syn,sum);break;
case -1: printf("\n ERROR;\n");break;
default: printf("(%d,%s)\n",syn,token);
}
}while(syn!=0);
getch();
}
void cffx()
{
m=0;
sum=0;
for(n=0;n<8;n++)
token[n]='\0';
ch=prog[p++];
while(ch==' ')
ch=prog[p++];
if(isalpha(ch))
{
while(isalpha(ch)||isdigit(ch))
{
token[m++]=ch;
ch=prog[p++];}
token[m++]='\0';
ch=prog[p--];
syn=10;
for(n=0;n<6;n++)
if(strcmp(token,rwtab[n])==0)
{
syn=n+1;
break;}}
else
if(isdigit(ch))
{
while(isdigit(ch))
{
sum=sum*10+ch-'0';
ch=prog[p++];}
ch=prog[p--];
syn=11;}
else
switch(ch){
case'<':m=0;token[m++]=ch;ch=prog[p++];
if(ch=='>'){
syn=21;
token[m++]=ch;}
else if(ch=='='){
syn=22;
token[m++]=ch;}
else{
syn=20;
ch=prog[p--];}
break;
case'>':m=0;token[m++]=ch;ch=prog[p++];
if(ch=='='){
syn=24;
token[m++]=ch;}
else{
syn=23;
ch=prog[p--];}
break;
case':':m=0;token[m++]=ch;ch=prog[p++];
if(ch=='='){
syn=18;
token[m++]=ch;}
else{
syn=17;
ch=prog[p--];}
break;
case'+':syn=13;
token[0]=ch;
break;
case'-':syn=14;
token[0]=ch;
break;
case'*':syn=15;
token[0]=ch;
break;
case'/':syn=16;
token[0]=ch;
break;
case'=':syn=25;
token[0]=ch;
break;
case';':syn=26;
token[0]=ch;
break;
case'(':syn=27;
token[0]=ch;
break;
case')':syn=28;
token[0]=ch;
break;
case'#':syn=0;
token[0]=ch;
break;
default:syn=-1;
}
}