As I asked in question header, without router can we share the internet with modem+hub or modem+switch?
Yes and no. Your isp will have to authorize your connection to obtain more than one IP address. Not knowing where you are from, I have no idea if your isp would, likely there would be additional charge if available. (In the USA typical home connections do not have this option, commercial customers likely have more options.)
The router will allow you to run your own private network. It will assign local IP addresses to your computers, and share a single external internet IP address among all devices connected to the network.
@Hasan In a true modem, you cannot just connect a switch or hub to the modem to share the Internet connection. This is because your ISP's router is probably programmed to give you only one IP address, and if you connect multiple computers via a switch, all of them will try to request an IP address (which your ISP will not allow). A router, on the other hand, will take the one IP address you are provided and use it to make requests on behalf of the computers behind it. This is something a modem+switch combo is not capable of doing. – user54791
That said, these days many hardware makers are putting router software into their modems, effectively turning the modem into a basic router so that you can connect a switch to a modem to share the Internet connection. Again, it's to make things more consumer-friendly. However, a true, "pure" modem will not allow you to do this. – user54791