AN UNEXPECTED MISTAKE OCCURRED by Huacoa

#include<stdio.h>
#include<string.h>
char prog[80],token[6];
char ch;
int syn,p,m,n,sum;
int scaner();
char * rwtab[6]={"begin","if","then","while","do","end"};
void main()
{
p=0;
printf("\nplease intput string:");
do
{
ch=getchar();
prog[p++]=ch;
}while(ch!='#');
p=0;
do
{
scaner();
switch(syn)
{
case 11:printf("(%d,%d)\n",syn,sum);break;
case -1:printf("input error\n"); break;
default:printf("(%d,%s)\n",syn,token);
}


}while(syn!=0);
getchar();
}
/*词法扫描程序：*/
int scaner()
{
for(n=0;n<8;n++)
token[n]=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<='9'&&ch>='0'))
{
    token[m++]=ch;
    ch=prog[p++];
    }
token[m++]='\0';
ch=prog[--p];
syn=10;
for(n=0;n<6;n++)
     if(strcmp(token,rwtab[n])==0)
     {
        syn=n+1;
        break;
        }
    }
else
     if((ch<='9'&&ch>='0'))
         {
         sum=0;
         while((ch<='9'&&ch>='0'))
         {
         sum=sum*10+ch-'0';
         ch=prog[p++];
         }
         ch=prog[--p];
         syn=11;
         }
     else
        switch(ch)

        
{
         case '<':m=0;token[m++]=ch;
                 ch=prog[p++];
                 if(ch=='>')
                 {
                    syn=21;
                    token[m++]=ch;
                    }
                    else
                        if(ch=='=')
                        {
                         syn=22;
                         token[m++]=ch;
                         }
                         else
                         {
                         syn=20;
                         ch=prog[--p];
                         }
         break;
         case '>':token[m++]=ch;
                 ch=prog[p++];
                 if(ch=='=')
                 {
                 syn=24;
                 token[m++]=ch;
                    }
                 else
                 {
                    syn=23;
                    ch=prog[--p];
                    }
         break;
         case ':':token[m++]=ch;
                 ch=prog[p++];
                 if(ch=='=')
                 {
                    syn=18;
                    token[m++]=ch;
                 }
                    else
                {

                
syn=17;
                     ch=prog[--p];
                     }
         break;
         case '+':syn=13;token[0]=ch;break;
         case '-':syn=14;token[0]=ch;break;
         case '*':syn=15;token[0]=ch;break;
         case '/':syn=16;token[0]=ch;break;
         case ':=':syn=18;token[0]=ch;break;
         case '<>':syn=21;token[0]=ch;break;
         case '<=':syn=22;token[0]=ch;break;
         case '>=':syn=24;token[0]=ch;break;
         case '=':syn=25;token[0]=ch;break;
         case ';':syn=26;token[0]=ch;break;
         case '(':syn=27;token[0]=ch;break;
         case ')':syn=28;token[0]=ch;break;
         case '#':syn=0;token[0]=ch;break;
         default:syn=-1;
         }return(syn);
     }