UVa 350: Pseudo-Random Numbers

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
using namespace std;

int is_in[10000];
int main()
{
int Z,I,M,L;
int Case=0;
while(cin >> Z >> I >> M >> L && M!=0)
{
Case++;
memset(is_in,0,sizeof(is_in));
int count=0,l=L;
while(1)
{
l = ((Z*l)%M+I)%M;
if(is_in[l]==0)	is_in[l]=1;
else if(is_in[l]==1) break;
}
int start_seed=l;
do
{
l = ((Z*l)%M+I)%M;
count++;
}while(l!=start_seed);
cout << "Case " << Case << ": " << count << "\n";
}
return 0;
}