Function add linked list

[kempofighter]

when I put second Doctor, Students take from the first Doctor
as,

Doctor 1
===> Student 1
===> Student 2

Doctor 2
===> Student 1
===> Student 2
===> Student 3
===> Student 4

Now, How do I create a function add_student?

I have no idea what that first statement means. Again - please state your requirements more clearly. What do you want a linked list of? students? Doctors? Both?