词法分析程序（C）

#include <stdio.h>
#include <string.h>  

char string[80],word[8],ch;
int type,p,i,n,sum;
char keyword[][6]={"begin","if","then","while","do","end"};    //关键字数组

void scaner(void);  

main()
{
    p=0;
    printf("\n\n请输入一个程序段(以‘#‘结束):\n");
    do{
            scanf("%c",&ch);
            string[p++]=ch;
    }while(ch!=‘#‘);
     printf("单词符号\t种别码 \n");
    p=0;
    do{
            scaner();
            switch(type)
            {
                case 11:
                    printf("   %-10d%5d\n",sum,type);
                break;
                case -1:
                    printf("有无法识别的字符\n");
                    return 0;
                break;
                default:
                printf("   %-10s%5d \n",word,type);
                break;
            }
        }while(type!=0);
 }  

void scaner(void)
{
    sum=0;
    for(i=0;i<8;i++)
       word[i++]= NULL;  

    ch=string[p++];
    i=0;  

    while((ch==‘ ‘)||(ch==‘\n‘))
        ch=string[p++];  

    if(((ch<=‘z‘)&&(ch>=‘a‘))||((ch<=‘Z‘)&&(ch>=‘A‘)))
     {
        while(((ch<=‘z‘)&&(ch>=‘a‘))||((ch<=‘Z‘)&&(ch>=‘A‘))||((ch>=‘0‘)&&(ch<=‘9‘)))
        {
            word[i++]=ch;
            ch=string[p++];
        }

     p--;
     type=10;                     //先将以字母开头的字符识别为标识符

        for(n=0;n<6;n++)
        if(strcmp(word,keyword[n])==0)    //关键字数组比较，相同则表示为关键字，种别码即为下标值加一
        {
            type=n+1;
            break;
        }
    }                                   

    else if((ch>=‘0‘)&&(ch<=‘9‘))
     {
        while((ch>=‘0‘)&&(ch<=‘9‘))
        {
            sum=sum*10+ch-‘0‘;    //将字符型转化为整形sum
            ch=string[p++];
        }
        p--;
        type=11;
     }  

    else                   //else语句内识别除关键字、标识符、数字以外的其他字符
    {
        switch(ch)
        {
        case ‘+‘:
            type=13;
            word[i++]=ch;
        break;  

        case ‘-‘:
            type=14;
            word[i++]=ch;
        break; 

         case ‘*‘:
            type=15;
            word[i++]=ch;
        break;  

        case ‘/‘:
            type=16;
            word[i++]=ch;
        break;  

        case ‘:‘:
            word[i++]=ch;
            ch=string[p++];
         if(ch==‘=‘)
           {
               type=18;
               word[i++]=ch;
           }
            else
            {
                type=18;
                p--;
            }
        break; 

        case ‘<‘:
            word[i++]=ch;
            ch=string[p++];
            if(ch==‘=‘)
            {
                type=21;
                word[i++]=ch;
            }
            else
            {
                type=20;
                p--;
            }
        break;  

        case ‘>‘:
            word[i++]=ch;
            ch=string[p++];
            if(ch==‘=‘)
            {
                type=24;
                word[i++]=ch;
            }
            else
            {
                type=23;
                p--;
            }
        break;

        case ‘=‘:
                type=25;
                word[i++]=ch;
        break;  

        case ‘;‘:
            type=26;
            word[i++]=ch;
        break;  

        case ‘(‘:
            type=27;
            word[i++]=ch;
        break;  

        case ‘)‘:
            type=28;
            word[i++]=ch;
        break;  

        case ‘#‘:
            type=0;
            word[i++]=ch;
        break;  

        default:
            type=-1;
        break;
        }
    }
        word[i++]=‘\0‘;                      //word字符数组变字符串
}