#include<stdio.h>
#include<string.h>
char input[200];//存放输入字符串
char token[5];//存放构成单词符号的字符串
char ch; //存放当前读入字符
int p; //input[]下标
int fg; //switch标记
int num; //存放整形值
//二维字符数组，存放关键字
char index[6][6]={"begin","if","then","while","do","end"};
main()
{
p=0;
printf("please intput string(End with '#'):\n");
do
ch=getchar();
input[p++]=ch;
}while(ch!='#');
scaner();
switch(fg)
case 11:printf("( %d,%d ) ",fg,num);break;
case -1:printf("input error\n"); break;
default:printf("( %d,%s ) ",fg,token);
}
}while(fg!=0);
getch(); //用于让程序停留在显示页面
/*词法扫描程序：*/
scaner()
int m=0;//token[]下标
int n;
//清空token[]
for(n=0;n<5;n++)
token[n]=NULL;
//获取第一个不为0字符
ch=input[p++];
while(ch==' ')ch=input[p++];
//关键字（标识符）处理流程
if((ch<='z'&&ch>='a')||(ch<='Z'&&ch>='A'))
while((ch<='z'&&ch>='a')||(ch<='Z'&&ch>='A')||(ch<='9'&&ch>='0'))
token[m++]=ch;
token[m++]='\0';
ch=input[--p];
fg=10;
for(n=0;n<6;n++)
if(strcmp(token,index[n])==0)//strcmp()比较两个字符串,相等返回0
fg=n+1;
break;
//数字处理流程
else if((ch<='9'&&ch>='0'))
num=0;
while((ch<='9'&&ch>='0'))
num=num*10+ch-'0';
fg=11;
//运算符界符处理流程
else
switch(ch)
case '<':
m=0;
if(ch=='>') //产生<>
fg=21;
else if(ch=='=') //产生<=
fg=22;
fg=20;
case '>':
if(ch=='=') //产生>=
fg=24;
else //产生>
fg=23;
case ':':
if(ch=='=') //产生:=
fg=18;
else //产生：
fg=17;
case '+':fg=13;token[0]=ch;break;
case '-':fg=14;token[0]=ch;break;
case '*':fg=15;token[0]=ch;break;
case '/':fg=16;token[0]=ch;break;
case ':=':fg=18;token[0]=ch;break;
case '<>':fg=21;token[0]=ch;break;
case '<=':fg=22;token[0]=ch;break;
case '>=':fg=24;token[0]=ch;break;
case '=':fg=25;token[0]=ch;break;
case ';':fg=26;token[0]=ch;break;
case '(':fg=27;token[0]=ch;break;
case ')':fg=28;token[0]=ch;break;
case '#':fg=0;token[0]=ch;break;
default:fg=-1;
}