简易的词法分析程序

Posted 2020-08-12

#include <stdio.h>
#include <string.h>
char prog[666],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‘;
    printf("感谢您使用本程序!");
}