/* begin if then while do end := + - * / < <= <> > >= = ; ( ) # 输入：所给文法的源程序字符串。 输出：二元组（syn，token或sum）构成的序列。 其中：syn为单词种别码； token为存放的单词自身字符串； sum为整型常数。 */ #include #include char prog[80]; char token[8]; char ch; int syn,p,m=0,n,sum=0; /* p是缓冲区prog的指针，m是token的指针*/ char *rwtab[6]={"begin","if","then","while","do","end"}; /* char prog[]="begin if then 2>3 end#"; */ void scaner(); int strcmpo(char a[],char b[]); void print(char a[]); int main() { p=0; printf("please input string: \n"); do{ch=getchar(); prog[p]=ch; p++; }while(ch!='#'); p=0; do { scaner(); switch(syn) { case 11: printf("(11,%d)\n",sum); break; case -1: print(token);printf("-error!\n"); break; default: printf("(%d,",syn); print(token); printf(")\n"); } }while (syn!=0); return 0; }/*end of main()*/ void scaner() { for(n=0;n<8;n++) token[n]='\0'; ch=prog[p]; 

p++; while(ch==' '||ch=='\n') /*接收空格*/ { ch=prog[p]; p++; } if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z')) /*标志符和关键字ID=letter（letter| digit）* */ { m=0; while((ch>='A'&&ch<='Z')||(ch>='a'&&ch<='z')||(ch>='0'&&ch<='9')) /*识别标志符*/ { token[m]=ch; m++; ch=prog[p]; p++; } token[m]='\0'; p--; syn=10; for(n=0;n<6;n++) /*识别关键字*/ { if(strcmpo(token,rwtab[n])==0) { syn=n+1; break; } } }/*end of if*/ else if(ch>='0'&&ch<='9') /*数字NUM=digit digit **/ { sum=0; while(ch>='0'&&ch<='9') { sum=sum*10+(int)ch-(int)'0'; ch=prog[p]; p++; } if(ch=='.') { ch=prog[p]; p++; int i=1; while(ch>='0'&&ch<='9') { sum+=((int)ch-(int)'0')*pow(0.1,i); ch=prog[p]; p++; i++; 

} } p--; syn=11; }/*end of else if*/ else /*识别运算符和界符*/ switch(ch) { case'<':m=0; token[m]=ch; ch=prog[p]; p++; if(ch=='>'){syn=21;m++;token[m]=ch;} else if(ch=='='){syn=22;m++;token[m]=ch;} else{p--;syn=20;} m++; token[m]='\0'; break; case'>':m=0; token[m]=ch; ch=prog[p]; p++; if(ch=='='){syn=24;m++;token[m]=ch;} else{syn=23;p--;} m++; token[m]='\0'; break; case':':m=0; token[m]=ch; ch=prog[p]; p++; if(ch=='='){syn=18;m++;token[m]=ch;} else{syn=17;p--;} m++; token[m]='\0'; break; case'+':syn=13; token[0]=ch; token[1]='\0'; break; case'-':syn=14; token[0]=ch; token[1]='\0'; break; case'*':syn=15; token[0]=ch; token[1]='\0'; break; case'/':syn=16; token[0]=ch; token[1]='\0'; break; 

case'=':syn=25; token[0]=ch; token[1]='\0'; break; case';':syn=26; token[0]=ch; token[1]='\0'; break; case'(':syn=27; token[0]=ch; token[1]='\0'; break; case')':syn=28; token[0]=ch; token[1]='\0'; break; case'#':syn=0; token[0]=ch; token[1]='\0'; break; default:syn=-1; token[0]=ch; token[1]='\0'; }/*end of switch*/ }/*end of scaner*/ int strcmpo(char a[],char b[]) /*比较两字符串是否相同*/ { int t=0; while((a[t]!='\0')&&(b[t]!='\0')&&(a[t]==b[t]))t++; if((a[t]=='\0')&&(b[t]=='\0'))return 0; else return 1; }/*end of strcmp*/ void print(char a[]) /*输出字符数组*/ { int t=0; while(a[t]!='\0') { printf("%c",a[t]); t++; } }/*end of print*/