#include<iostream>
using namespace std;
int main()
{
int Z,I,M,L,i,n,check,point,a[10000];
n=1;
while(cin>>Z>>I>>M>>L)
{
if(Z==0&&I==0&&M==0&&L==0)break;
point=0;check=1;
while(check)
{
a[point++]=L;
L=(Z*L+I)%M;
for(i=0;i<point;i++)
if(a[i]==L)
{
check=0;break;
}
}
cout<<"Case "<<n++<<": "<<point-i<<endl;

}
}

更快的:

#include <bits/stdc++.h>

using namespace std;
int main(int argc, char** argv){
//ios_base::sync_with_stdio(false);
cin.tie(0);
int a[4],b=1,c,d,e[10000],g;
while(cin>>a[0]>>a[1]>>a[2]>>a[3]&&a[0]+a[1]+a[2]+a[3]!=0&&b++){
g=1;
d=0;
e[d]=a[3];
while(g){

e[d]=(a[0]*e[d-1]+a[1])%a[2];
for(int f=0;f<=d-1;f++){
if(e[f]==e[d]){
f=d;
g=0;
}
}
d++;
}
cout<<"Case "<<b-1<<": "<<d-1<<'\n';
}
}