简单语法分析器实现

#include <string.h>

#include <ctype.h>

char prog[80],token[8];

char ch;

int syn,p,m,n,kk,sum=0;

char *rwtab[6]={"begin","if","then","while","do","end"};

int lrparser();

int yucu();

int statement();

int expression();

int term();

int factor();

void scanner()

{

m=0;

for(n=0;n<8;n++)

token[n]=NULL;

ch=prog[p++];

while(ch==‘ ‘)ch=prog[p++];

if(isalpha(ch))//字母字符

{

while(isdigit(ch)||isalpha(ch))//字母或数字字符

{

token[m++]=ch;

ch=prog[p++];

}

token[m++]=‘\0‘;p--;syn=10;

for(n=0;n<6;n++)

if(strcmp(token,rwtab[n])==0)

{

syn=n+1;

break;

}

}

else if(isdigit(ch))//数字字符

{

sum=0;

while(isdigit(ch))//shuzi

{

sum=sum*10+ch-‘0‘;

ch=prog[p++];

}

p--;

syn=11;

}

else

switch(ch)

{

case ‘<‘: m=0;

token[m++]=ch;

ch=prog[p++];

if(ch==‘>‘)

{

syn=22;

token[m++]=ch;

}

else 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=18;

token[m++]=ch;

}

else

{

syn=17;

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;

}

}

int lrparser()//分析语句串开始结束

{

//scanner();//读取下一个单词符号

if(syn==1)

{

scanner();

yucu();

if(syn==6)

{

scanner();

if(syn==0&&(kk==0))

printf("Success!");

}

else{

if(kk!=1)

printf("lose end!");

kk=1;

}

}

else{

printf("lose begin!");

kk=1;

}

return 1;

}

int yucu()

{

statement();

while(syn==26)//分号，

{

scanner();

statement();

}

return 1;

}

int statement()//赋值语句分析

{

if(syn==10)//标示符

{

scanner();

if(syn==18)//赋值号:=

{

scanner();

expression();

}

else{printf(":=错误!");kk=1;}

}

return 1;

}

int expression()

{

term();

while(syn==13||syn==14)

{

scanner();

term();

}

return 1;

}

int term()//运算符识别

{

factor();

while(syn==15||syn==16)

{

scanner();

factor();

}

return 1;

}

int factor()

{

if(syn==11||syn==10)

scanner();

else if(syn==27)

{

scanner();

expression();

if(syn==28)

scanner();

else

{

printf("‘)‘ERROR!");

kk=1;

}

}

else

{

printf("biaodashicuowu");

}

return 1;

}

void main()

{

p=0;

printf("\n please input string:\n");

do{

ch=getchar();

prog[p++]=ch;

}while(ch!=‘#‘);

p=0;

scanner();

lrparser();