C语言实现词法分析
所用软件
Dev-C++
or
Microsoft Visual C++
代码块
#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"};
scaner();
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 need input a string\n");
getch();
exit(0);
default: printf("( %-10s%5d )\n",token
,syn
);
break;
}
}while(syn
!=0);
getch();
}
scaner()
{ 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';
}
使用方法
直接创建一个C语言文件，将代码块复制粘贴，使用编译器打开即可。
效果图
