Know the address of a switch

It's okay, I have my answer:

D-link DES-1210-28 switch manageable 24 ports.

I never questioned how to find the IP address of a manageable switch. So I'll let others answer.

PS: on another model I read:

Configuration is done via a web interface. An installation program is also provided, specifically to detect its IP address necessary for its configuration. Installing the software will first allow you to determine its IP address. Once the device is detected, the window will allow us to modify the IP settings via the configuration Setting command. The chosen IP address must be within the same range as the entire network or at least that of the connected PC if you are working with static IP addresses. Once this configuration is completed, you can access the configuration of the manageable switch DGS-1216T through your preferred browser or by using the Web Access button in the configuration window. The initial display gives a summary of the device's configuration.

So I think you probably need some kind of program for it to find the switch's address.
EDIT: indeed it must be something along those lines, the response from choubaka goes in that direction as well.

By default, the switch's IP address is 10.90.90.90, but I changed it during the installation to be in the same IP class as the rest of the network. I thought I had set it to 192.168.0.254, but that's not it... So I'm searching!

In any case, thank you! I didn't know there were all these software options; it's useful! So I got a LAN chat software because I've been looking for one for a long time, and the ones I came across were useless...

you can download an IP scanner
the link: www.eusing.com/ipscan/free_ip_scanner.htm