Lex : Number is prime or not

%{
#include<stdio.h>
#include<stdlib.h>
int flag,c,j;
%}
%%
[0-9]+ {c=atoi(yytext);}
%%
int main()
{
yylex();
if(c==2)
{
printf("\n Prime number");
}
else if(c==0 || c==1)
{
printf("\n Not a prime number");
}
else
{
for(j=2;j<c;j++)
{
if(c%j==0)
flag=1;
}
if(flag==1)
printf("\n Not a prime number");
else if(flag==0)
printf("\n Prime number");
}
}