c - Finding prime numbers is giving me errors -

i wanted print divisors of given range of numbers. works alright. when try modify put **** @ end of prime number's divisors acts bizarre.

#include <stdio.h> int main() {     int     a,start,rounds,b,c,k=0;      printf("please enter number start :");     scanf("%d",&start);     printf("please enter how many numbers want print number :");     fflush(stdin);     scanf("%d",&rounds);      for(a=start;a<=start+rounds;a++)     {          printf("\n\nthe divisors of number :%d \n",a);           for(b=1;b<=a;b++)          {              c=a%b;              if(!c)              {                   k++;                   printf("%d\n",b);              }           }           //printf("%d",k);           if((k==2)||(k==1))              printf("***\n");     }     getchar();     return 0; } 

ps:- trick used find prime number counting how many printf statement has been executed before loop ends. there wrong it? when remove // printf statement prints below.

start=========>k    1   =========>1    2   =========>3    3   =========>5    4   =========>8    5   =========>10 

why that?

if((k==2)&&(k==1))

there no way in todays computers k can 2 and 1 @ same time. maybe meant if k 2 or k 1 ?