0929作业

1词法分析器的功能 1）输入源程序 2）从左至右地对源程序进行扫描，按照语言的词法规则识别各类单词，并产生相应单词的属性字

2.

单词符号	种别码	单词符号	种别码
begin	1	:	17
if	2	:=	18
then	3	<	20
while	4	<=	21
do	5	<>	22
end	6	>	23
l(l|d)*	10	>=	24
dd*	11	=	25
+	13	;	26
-	14	(	27
*	15	)	28
/	16	#	0

3.用文法描述词法规则

<字母> A a|b|c|……y|z

<数字> 
A→1|2|3|4|5|6|7|8|9
S→A|SA|SA0 
<整数常数>
A→1|2|3|4|5|6|7|8|9
S→A|SA|SA0 
<标识符>
A→a|b|c|……y|z
B→0|1|2|3|4|5|6|7|8|9
S→A|SB
<关键字>
S→if|else|while|do|for|int|char|……
<运算符>
S→+|-|x|/|=|#|<|>|<=|>=|：=
<界符>
S→(|)|,|;|.

#include <stdio.h>  
#include <string.h>  
  
char prog[80],token[8],ch;  
int syn,p,m,n,sum;  
char *rwtab[6]={"begin","if","then","while","do","end"};  
   
void scaner(void);  
  
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();  
                    return 0;  
                break;  
                  
                default:   
                printf("( %-10s%5d )\n",token,syn);  
                break;  
            }  
        }while(syn!=0);  
    //getch();  
    return 0;
 }  
  
void scaner(void)  
{    
    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';  
}