0xN35T:
How can I connect 4 7-segment displays to Arduino. Maybe via other chip.
Yes. I use a 20mm common cathode 4x7 with a MAX7221 multiplexer.
Article is here Arduino Playground - HomePage
Example is here Usable 4x7 LED with 7221 - LEDs and Multiplexing - Arduino Forum
There may be more elegant code around, but it isn't easy to find.