实验一

实验一、词法分析

专业  商业软件工程 姓名 刘宇  学号 201504040153

一、        实验目的

 

•      编制一个词法分析程序

二、        实验内容和要求

–        输入：源程序字符串

–     输出：二元组（种别，单词本身）

–     待分析语言的词法规则

三、        实验方法、步骤及结果测试

 

#include <stdio.h>

#include <string.h>

#include<conio.h>

#include <process.h>

char prog[80],token[8],ch;

int syn,p,m,n,sum;

char *rwtab[6]={"begin","if","then","while","do","end"};

 scaner();

main()

{p=0;

 printf(" 请输入字符串，以 # 结束:");

 do{

    scanf("%c",&ch);

    prog[p++]=ch;

    }while(ch!='#');

 p=0;

 do{

    scaner();

    switch(syn)

     {case 11:printf("( %-10d%5d ) ",sum,syn);

          break;

      case -1:printf("字符串输入错误") ;

          getch();

          exit(0);

      default: printf("< %-10s%5d > ",token,syn);

          break;

      }

    }while(syn!=0);

    getch();

 }

 scaner()

 {  sum=0;

    for(m=0;m<8;m++)token[m++]=NULL;

    ch=prog[p++];

    m=0;

    while((ch==' ')||(ch==' '))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++]='';

    }

运行截图：

 

 

 

 

四、        实验总结

对词法分析语法如何转换成代码还不太熟练，问了同学还翻了书，最后写出了程序