实验报告（3）-语法分析

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

char prog[100],token[8],ch; 
char *rwtab[6]={"begin","if","then","while","do","end"};  
int syn,p,m,n,sum;

void E();            //E->TE1;
void E1();           //E1->+TE1|-TE1|ε
void T();            //T->FT1
void T1();            //T1->*FT1 |/FT1|ε
void F();            //F->(E) | i

error();
void scaner();

int main()  
{  
    
    p=0;  
    printf("\nplease input a string (end with ‘#‘): \n");  
  
   do  
    {  
        scanf("%c",&ch);  
        prog[p++]=ch;  
    }while(ch!=‘#‘); 
    
    p=0;
    scaner();
    E();

}  


void E()
{
    T();
    E1();  
}

void E1()
{
    if((syn==13)||(syn==14))
    {
        scaner();
        T();
        E1();
        
    }
    else 
    {
        if(syn!=28 && syn!=0)
        error();
    }
}

void T()
{
    F();
    T1();
}
void T1()
{
    if((syn==15)||(syn==16))
    {
       scaner();
       F();
       T1();
    }
    else 
    {
        if(syn!=28 && syn!=0 && syn!=13)
        error();
    }
    
}
void F()
{
    if(syn==27)
    {
        scaner();
        E();
        if(syn==28)
        {
            scaner();
            E();
            if(syn==0)
                printf("\nTrue!\n");
        }
        else
        error();
    }
    else if(syn==11||syn==10)
        scaner();
}

error()
{
    printf("\n Syn Error!\n");
}

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