When working with seven segment displays with a common pin (either anode or cathode) you need to avoid using delay. The way the displays work is by flashing one digit really quickly, then flashing the next digit. When you flash the digits really quickly your eye can't tell. It is like using PWM on a LED (actually the exact same thing).
Try something similar to this psudeo code
void loop{
Check if time to update value (update is needed)
display segment 1
display segment 2
display segment 3
display segment 4
}
This is called a state machine if you want to learn more.