~cpp
#include <stdio.h>
#include <math.h>
int main(void)
{
int num, sqrt_num, n, result=0;;
printf(" : ");
scanf("%d", &num);
for( ; num; result=0)
{
if(num>0)
{
sqrt_num = (int)sqrt((double)num);
for(n=2; n<=sqrt_num; n++)
{
if(!(num%n))
{
result = 1;
break;
}
}
printf(" %d : %s\n\n", num, result ? " ." : ".");
}
printf(" : ");
scanf("%d", &num);
}
return 0;
}









