uva solve problem 10490_mr.Azad and his son

#include<stdio.h>
#include<math.h>
int main()
{
   int a[100],i,j,k,p,b[100];
    for(i=2;i<=31;i++)
    {
        b[i]=0;
    a[i]=0;
    }
    a[1]=1;
    b[11]=1;
    b[23]=1;
    b[29]=1;
    p=sqrt(31);
    for(j=2;j<=p;j++)
    {
        for(k=2;j*k<31;k++)
        {
        a[j*k]=1;
        b[j*k]=1;
        }
    }

    int n,m;
    long long int x,z,result;
    while(scanf("%d",&n)!=EOF)
    {
        if(n==0)
        break;
        if(a[n]==0)
        {
         m=n-1;
         x=pow(2,m);
         z=pow(2,n);
         result=x*(z-1);
         if(b[n]==0)
         printf("Perfect: %lld!\n",result);
         else
         printf("Given number is prime. But, NO perfect number is available.\n");
        }
        else
        printf("Given number is NOT prime! NO perfect number is available.\n");
    }
    return 0;

}