I am working with the DE10-Nano board. After building the new kernel (4.14.x) below folder exists in the $HOME directory:
This contains the below files:
blink hello scroll_client syschk toggle
Where do i find the C Source code that is used to generate these programs?
directory intelFPGA is created during isntalation of Intel Quartus Prime or just Intel Embedded Software Development Studio. Programmes like blink are not made by building kernel (although You do not compile it with some tool which has compile all of that as a tutorial, e.g. Yocto project with some default meta-layers).
Some source code of example prorammes could be found at directory $HOME/intelFPGA/18.0/embedded/examples/software. I am sorry, I am not sure if this contain a source code for programs You mentioned or not.
Another good place to looking for source code for examples is https://rocketboards.org/foswiki/Documentation/AlteraSoCWorkshopSeries.
Hope this will help You a bit.
The source code i was looking for in the above question is in the below path:
Though this folder contains many more examples for reference.