How to get the applications installed in the system using c# code?
Might I suggest you take a look at WMI (Windows Management Instrumentation). If you add the System.Management reference to your C# project, you'll gain access to the class `ManagementObjectSearcher', which you will probably find useful.
There are various WMI Classes for Installed Applications, but if it was installed with Windows Installer, then the Win32_Product class is probably best suited to you.
ManagementObjectSearcher s = new ManagementObjectSearcher("SELECT * FROM Win32_Product");