语法分析程序

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char prog[100],ch,token[8];
int p=0,syn,n,i;
char *keyword[6]={"begin","then","if","while","do","end"};
void scaner();
void Irparse();
void statement();
void expression_r();
void term();
void factor();


void main()
{
int select=-1;
p=0;
printf("please input sentence, end of '#' !
");
do
{
ch=getchar();
prog[p++]=ch;
}while(ch!='#');
p=0;

printf("请输入1 或 2 
 1.词法分析
 2.语法分析
");
scanf("%d",&select);
if(select==1)
{ 
do
{
scaner();
switch(syn)
{

case -1:printf("词法分析 出错
");break;
default :printf("<%d,%s>
",syn,token);break;
} 
}while(syn!=0);
printf("词法分析 成功
");
}
else if(select==2) 
{
scaner();
if(syn==1)
{Irparse();}//begin
else
{printf("语法分析出错! 请检查begin关键字
");return;}
if(syn==6)//end
{
scaner();
if(syn==0)
{
printf("恭喜 语法分析 成功
");
}
else
{printf("语法分析出错! 请检查是否缺少'#'
");}
}
else{printf("语法分析出错! 请检查是否缺少'end'
");}


}
getchar();

}
void scaner()
{


for(n=0;n<8;n++)
{token[n]='';}
n=0;
ch=prog[p++];
while(ch==' '){ch=prog[p++];}

if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z'))
{
do{
token[n++]=ch;
ch=prog[p++];
}while((ch>='a'&&ch<='z')||(ch>='a'&&ch<='z')||(ch>='0'&&ch<='9'));
syn=10;

for(n=0;n<6;n++)
{if(strcmp(token,keyword[n])==0)
{
syn=n+1;

}
}
p--;
//return;
}
else if(ch>='0'&&ch<='9')
{
p--;
do
{
token[n++]=prog[p++];
ch=prog[p];
}while(ch>='0'&&ch<='9');
syn=11;


return;
}
else
{

//ch=prog[p++];
switch(ch)
{
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=17;token[0]=ch;
ch=prog[p++];
if(ch=='='){token[1]=ch;syn++;}
else p--;
break;
case '<':syn=20;token[0]=ch;
ch=prog[p++];
if(ch=='>'){token[1]=ch;syn++;}
else if(ch=='='){token[1]=ch;syn=syn+2;}
else p--;
break;
case '>':syn=23;token[0]=ch;
ch=prog[p++];
if(ch=='='){token[1]=ch;syn++;}
else p--;
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: printf("词法分析出错! 请检查是否输入非法字符
");syn=-1;break;

}

//return;
}

}


void Irparse()
{
scaner();
statement();
while(syn==26)//;
{
scaner();
statement();
}

}
void statement()
{
if(syn==10)
{
scaner();
if(syn==18)
{
scaner();
expression_r();
}
else
{
printf("语法分析出错! 请检查表达式是否正确
");return;
}
}
else
{
printf("语法分析出错! 请检查语句是否正确
");return;
}
}

void expression_r()
{
term();
while(syn==13||syn==14)//+ -
{
scaner();
term();
}
}

void term()
{
factor();
while(syn==15||syn==16)//* /
{
scaner();
factor();
}
}
void factor()
{
if(syn==10||syn==11)
{
scaner();
}
else if(syn==27)
{
scaner();
expression_r();
if(syn==28)
{
scaner();
}
else {printf("语法分析出错! 请检查是否缺少')'
");return;}
}
else {printf("语法分析出错! 请检查是否输入非法字符
");return;}

}