1_2.cpp

实验目的：用c语言对一个简单语言的子集编制一个一遍扫描的编译程序

#include <stdio.h> 
#include <string.h> 

char prog[80],token[8]; 
char ch; 
int syn,p,m,n,sum; 
char *rwtab[6]={"begin","if","then","while","do","end"}; 

void scaner(); 

void main(){ 
p=0; 
printf("\n please input string;\n"); 
do { 
scanf("%c",&ch); 
prog[p++] = ch; 
}while (ch!='#'); 
p=0; 
do{ 
scaner(); 
switch(syn) { 
case 11: printf ("(syn,%d)\n",sum); break; 
case -1:printf("error!\n");break; 
default:printf("(%d,%s)\n",syn,token); 
} 
}while (syn!=0); 
} 

void scaner(){ 
for(n=0;n<8;n++) token[n]=NULL; 
ch = prog[p++]; 
while(ch==' ') 
ch = prog[p++]; 
if(ch>='a'&&ch<='z'){ 
m = 0; 
while((ch>='a'&&ch<='z')||(ch>='0'&&ch<='9')){ 
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(ch>='0'&&ch<='9'){ 
while (ch>='0'&&ch<='9'){ 
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=21; 
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; 
} 
}