a bout IP addresses

Why two copmuters after disconnecting them from a network and reconnecting them togther they would have IP addresses?

to communicate.

to communicate.
as simple as that man!

1.  Why.  Either the computers are manually configured with "static" IP addresses or they end up with "APIPA" IP addresses through automatic self-assignment.

2.  I can think of four ways an IP address is set on the computer:
    a.  Automatic assignment via Dynamic Host Configuration Protocol (DHCP)
    b.  Automatic self-assignment from APIPA range
    c.  Static assignment (manually set)
    d.  Bootstrap Protocol (BOOTP) used to obtain an IP address from a configuration server.

3.  If the computer is configured to "Obtain an IP address automatically" one of two things will happen:
     a.  It will broadcast a request for an IP address and a DHCP server will respond with one.
     b.  It will broadcast a request for an IP address and DHCP server(s) are either not available or unable to provide one.  In that case, Windows being Windows will assign itself an Automatic Private IP Addressing (APIPA) address from within the APIPA range (169.254.0.0/16).

4.  Reference(s):
     Dynamic Host Configuration Protocol (DHCP)
     Link-local address
     Bootstrap Protocol (BOOTP)

Thank you all. I think the answer as dahlarbear said is because of APIPA.
Thank you a lot and special thanks for you dahlarbear.

You're welcome.