Sql server data syncronization

Question

Hi

I have developed program using sql server as a backend database using c# (windows application), the thing is that client needs to work online and when system is connected through internet all the data goes online and vice versa.

Kindly suggest appropriate code to sync the data faster either it is done by sql server or programatically.

And if the program is used by more than 1 system, then data should also be sync from online to offline database.