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词法编译-201506110151-董广枢
#include<stdio.h>
#include<string.h>
#include<iostream.h>
char prog[80],token[8];
char ch;
int syn,p,m=0,n,row,sum=0;
char *rwtab[6]={"begin","if","then","while","do","end"};
void scaner()
{
/*
共分为三大块，分别是标示符、数字、符号，对应下面的 if else if 和 else
*/
for(n=0;n<8;n++) token[n]=NULL;
ch=prog[p++];
while(ch==‘ ‘)
{
ch=prog[p];
p++;
}
if((ch>=‘a‘&&ch<=‘z‘)||(ch>=‘A‘&&ch<=‘Z‘)) //可能是标示符或者变量名
{
m=0;
while((ch>=‘0‘&&ch<=‘9‘)||(ch>=‘a‘&&ch<=‘z‘)||(ch>=‘A‘&&ch<=‘Z‘))
{
token[m++]=ch;
ch=prog[p++];
}
token[m++]=‘\0‘;
p--;
syn=10;
for(n=0;n<6;n++) //将识别出来的字符和已定义的标示符作比较，
if(strcmp(token,rwtab[n])==0)
{
syn=n+1;
break;
}
}
else if((ch>=‘0‘&&ch<=‘9‘)) //数字
{
{
sum=0;
while((ch>=‘0‘&&ch<=‘9‘))
{
sum=sum*10+ch-‘0‘;
ch=prog[p++];
}
}
p--;
syn=11;
if(sum>32767)
syn=-1;
}
else switch(ch) //其他字符
{
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=23;
p--;
}
break;
case‘>‘:m=0;token[m++]=ch;
ch=prog[p++];
if(ch==‘=‘)
{
syn=24;
token[m++]=ch;
}
else
{
syn=20;
p--;
}
break;
case‘:‘:m=0;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;
case‘\n‘:syn=-2;break;
default: syn=-1;break;
}
}
int main()
{
p=0;
row=1;
cout<<"Please input string:"<<endl;
do
{
cin.get(ch);
prog[p++]=ch;
}
while(ch!=‘#‘);
p=0;
do
{
scaner();
switch(syn)
{
case 11: cout<<"("<<syn<<","<<sum<<")"<<endl; break;
case -1: cout<<"Error in row "<<row<<"!"<<endl; break;
case -2: row=row++;break;
default: cout<<"("<<syn<<","<<token<<")"<<endl;break;
}
}
while (syn!=0);
}
词法编译-201506110151-董广枢