词法分析

#include<stdio.h>

#include<string.h>

#include<ctype.h>

#define M 1000

struct key

{

    char g[20];

};

typedef struct key KEY;

int main()

{

    KEY k[6];

    int i=0,j=0;

    char a[M],b[M];

    strcpy(k[0].g,"begin");

    strcpy(k[1].g,"if");

    strcpy(k[2].g,"then");

    strcpy(k[3].g,"while");

    strcpy(k[4].g,"do");

    strcpy(k[5].g,"end");

 

    printf("请输入源程序: ");

    gets(a);

    while(a[i]!='')

    {

        j=0;

        if((isalpha(a[i]))||(a[i]=='_'))

        {

            while((a[i]!=' ')&&(a[i]!=''))

            {

                if((isalpha(a[i]))||(isdigit(a[i])))

                {

                 b[j]=a[i];

                 j++;

                 i++;

                }

                else

                    break;

            }

            if((a[i]==' ')||(a[i]==''))

            {

                b[j]='';

                if(strcmp(b,k[0].g)==0)

                    printf("begin 种别码   1 ");

                else if(strcmp(b,k[1].g)==0)

                    printf("if   种别码   2 ");

                else if(strcmp(b,k[2].g)==0)

                    printf("then 种别码   3 ");

                else if(strcmp(b,k[3].g)==0)

                    printf("while 种别码   4 ");

                else if(strcmp(b,k[4].g)==0)

                    printf("do   种别码   5 ");

                else if(strcmp(b,k[5].g)==0)

                    printf("end  种别码   6 ");

                else

                    printf("%s  种别码   10 ",b);

            }

            else

            {

                b[j]='';

                printf("%s   种别码       10 ",b);

                i--;

            }

        }

 

        else if(isdigit(a[i]))

        {

            j=0;

            while(isdigit(a[i]))

            {

                 b[j]=a[i];

                 j++;

                 i++;

            }

            b[j]='';

            printf("%s    种别码    11 ",b);

            i--;

        }

        else

        {

            switch(a[i])

            {

            case '+':

                printf("%c   种别码   13 ",a[i]);break;

            case '-':

                printf("%c   种别码   14 ",a[i]);break;

            case '*':

                printf("%c   种别码   15 ",a[i]);break;

            case '/':

                printf("%c   种别码   16 ",a[i]);break;

            case ':':

                if(a[i+1]=='=')

                {   printf(":=   种别码   18 ");i++;break;}

                else

                {   printf("%c   种别码   17 ",a[i]);break;}

            case '<':

                if(a[i+1]=='=')

                {   printf("<=   种别码   21 ");i++;break;}

                if(a[i+1]=='>')

                {   printf("<>   种别码   22 ");i++;break;}

                else

                    printf("%c   种别码   20 ",a[i]);break;

            case '>':

                if(a[i+1]=='=')

                {   printf(">=   种别码   24 ");i++;break;}

                else

                    printf("%c   种别码   23 ",a[i]);break;

            case '=':

                printf("=    种别码    25 ");break;

            case ';':

                printf(";   种别码    26 ");break;

            case '(':

                printf("(   种别码   27 ");break;

            case ')':

                printf(")   种别码   28 ");break;

            case '#':

                printf("#   种别码   0 ");break;

            default:

                printf("%c   语法错误! ",a[i]);break;

            }

        }

 

        i++;

    }

}