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:\n");

    gets(a);

    while(a[i]!='\0')

    {

        j=0;

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

        {

            while((a[i]!=' ')&&(a[i]!='\0'))

            {

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

                {

                 b[j]=a[i];

                 j++;

                 i++;

                }

                else

                    break;

            }

            if((a[i]==' ')||(a[i]=='\0'))

            {

                b[j]='\0';

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

                    printf("begin\t种别码   1\n");

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

                    printf("if   \t种别码   2\n");

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

                    printf("then \t种别码   3\n");

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

                    printf("while\t种别码   4\n");

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

                    printf("do   \t种别码   5\n");

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

                    printf("end  \t种别码   6\n");

                else

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

            }

            else

            {

                b[j]='\0';

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

                i--;

            }

        }

 

        else if(isdigit(a[i]))

        {

            j=0;

            while(isdigit(a[i]))

            {

                 b[j]=a[i];

                 j++;

                 i++;

            }

            b[j]='\0';

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

            i--;

        }

        else

        {

            switch(a[i])

            {

            case '+':

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

            case '-':

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

            case '*':

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

            case '/':

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

            case ':':

                if(a[i+1]=='=')

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

                else

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

            case '<':

                if(a[i+1]=='=')

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

                if(a[i+1]=='>')

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

                else

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

            case '>':

                if(a[i+1]=='=')

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

                else

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

            case '=':

                printf("=    \t种别码    25\n");break;

            case ';':

                printf(";   \t种别码    26\n");break;

            case '(':

                printf("(   \t种别码   27\n");break;

            case ')':

                printf(")   \t种别码   28\n");break;

            case '#':

                printf("#   \t种别码   0\n");break;

            default:

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

            }

        }

 

        i++;

    }

}