The latter two are interactive files .
Files are typically the principal means by which to interact with a program.
Before you can perform many of the operations on a file, the file must be opened . Opening a file associates it with a stream , a data structure within the Standard C library that glosses over many differences among files of various kinds. The library maintains the state of each stream in an object of type FILE . The target environment opens three files prior to program startup . You can open a file by calling the library function fopen with two arguments.