1.词法分析程序的功能
I:对字符串表示的源程序
P:根据词法规则从左到右进行扫描和分解
O：识别出一个一个具有独立意义的单词符号以供语法分析之用
E：发现语法错误，则返回出错信息
2.符号与种别码的对照表
3.词法规则
4.代码与运行结果截图
#include#include void scaner();main(){ int p=0,row=1; char prog[80],token[8],ch; int syn,m,n,sum; char *rwtab[6]={ "begin","if","then","while","do","end"}; printf("词法分析\n"); printf("请输入一段程序(以#结束):"); do{ scanf("%c",&ch); prog[p++]=ch; }while(ch!='#'); printf("词法分析结果如下:"); do{ scaner(ch,prog,token); switch(syn) { case 11: printf("( %-10d%5d )\n",sum,syn); break; case -1: printf("you have input a wrong string\n"); return 0; break; default: printf("( %-10s%5d )\n",token,syn); break; } }while(syn!=0); }void scaner(char ch, char prog[80],char token[8],) { int 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'; }