cffx.c

编译原理词法分析

# include <stdio.h>
# include <string.h>
char prog[80],token[8];
char ch;
int syn,p,m,n,sum=0;
char *rwtab[6]={"begin","if","then","while","do","end"};
void scaner();

main()
{
    p=0;
    printf("\n please input string:\n");
    do{
        scanf("%c",&prog[p++]);
    }while(prog[p-1]!='#');
    p=0;
    do{
        scaner();
        switch(syn)
    	{
        case 11:printf("(11,%d) ",sum);break;
        case -1:printf("error! ");break;
        default:printf("(%d,%s) ",syn,token);
        getch();
    	}
    }while(syn!=0);
}

void scaner()
{
    for(n=0;n<8;n++)
        token[n]=NULL;
    sum=0;
    ch=prog[p++];
    while(ch==' ')
        ch=prog[p++];
    if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z'))
    {
        m=0;
        while((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z')||(ch>='0'&&ch<='9'))
    	{
    		
            token[m++]=ch;
            ch=prog[p++];
    	}
        token[m++]='\0';
        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 '<':
        		m=0;
                token[m++]=ch;
                ch=prog[p++];
                if(ch=='>')
        		{
            		syn=21;
                    token[m++]=ch;
        		}
                else if(ch=='=')
        		{
            		syn=22;
                    token[m++]=ch;
        		}
        		else
        		{
            		syn=20;
                    p--;
        		}
            	break;
            case '>':
        		m=0;
                token[m++]=ch;
                ch=prog[p++];
                if(ch=='=')
        		{
            		syn=24;
                    token[m++]=ch;
        		}
        		else
        		{
            		syn=23;
                    p--;
        		}
            	break;
            case ':':
        		m=0;
                token[m++]=ch;
                ch=prog[p++];
                if(ch=='=')
        		{
            		syn=18;
                    token[m++]=ch;
        		}
        		else
        		{
            		syn=17;
                    p--;
        		}
            	break;
            case'+':syn=13;token[0]=ch;break;
            case'-':syn=14;token[0]=ch;break;
            case'*':syn=15;token[0]=ch;break;
            case'/':syn=16;token[0]=ch;break;
            case'=':syn=25;token[0]=ch;break;
            case';':syn=26;token[0]=ch;break;
            case'(':syn=27;token[0]=ch;break;
            case')':syn=28;token[0]=ch;break;
            case'#':syn=0;token[0]=ch;break;
            default:syn=-1;
            }
    	}
    }

}