• 词法分析程序


    一、功能

    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。

    二、符号与种别码对照表

    单词符号          种别码   单词符号     种别码

    begin                1         :         17

    If                   2         :=        18

    Then                3         <          20

    While               4         <>          21

    Do                  5         <=         22

    end                 6         >          23

    lettet(letter|digit)*  10         >=        24

    dight dight*           11        =          25

    +                   13         ;         26

    —                  14          (          27

    *                   15           )         28

    /                   16          #           0

    三、词法规则

    代码

    #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("\n please input a string(end with '#'):/n");
    do{
    scanf("%c",&ch);
    prog[p++]=ch;
    }while(ch!='#');

    p=0;
    do{
    scaner();
    switch(syn)
    {case 11:printf("( %-10d%5d )\n",sum,syn);
    break;
    case -1:printf("you have input a wrong string\n");
    getch();
    exit(0);
    default: printf("( %-10s%5d )\n",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=='\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';
    }
    }

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  • 原文地址:https://www.cnblogs.com/SOLARLKS/p/5924055.html
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