IP addresses are very dynamic. It's not decided by your computer at all, but more due to random variations at your internet service provider.
Some people are more susceptible to IP address change than others.
It's your ISP, which assigns a dynamic IP address to your account. If you're using a dial-up internet account, it will change whenever to log on. If you're using an always on account, it will chang whenever you reset your modem, or when the ISP chooses.
There are two types of IP addresses one is static and other one is dynamic. In most of the cases we use dynamic. I think you are also using dynamic address. You can choose to use static IP address, but that is not recommended as dynamic IP address use is having some advantages.
1st commet Right
3rd Unknown and this is the person who did Why.
What do you think?