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';  }