WHAT ARE LIBRARY FUNCTIONS AND THEIR USE IN C LANGUAGE? CAN WE WRITE OUR OWN FUNCTIONS AND INCLUDE THEM IN C LIBRARY?

Library functions in C language are inbuilt functions which are grouped together and placed in a common place called library. The use of library function is to get the pre-defined output instead of writing our own code to get those outputs.

Yes. We can write our own functions and include them in C library.