Check this code
string sEnrollNumber = "";
string sName = "";
string sPassword = "";
int iPrivilege = 0;
bool bEnabled = false;
int uCount=0;
axCZKEM1.EnableDevice(1, false);
axCZKEM1.ReadAllUserID(1);
while (axCZKEM1.SSR_GetAllUserInfo(1, out sEnrollNumber, out sName, out sPassword, out iPrivilege, out bEnabled))
{
uCount++;
}