The directive #include plugs content of the indicated file in text of the program. This directive has two forms:
#include "file name"
#include <file name>

The file name must correspond to the agreements of the operating system and can consist either only of the file name or from the file name with an antecedent to him by a route. If the file name is indicated in quotation marks, then the search of file comes true in accordance with the set route, and at his absence in a current directory. If the file name is set in angular brackets, then file man-hunted in the standard directories of the operating system, set by a command PATH. A directive #include can be inlaid, i.e. in the included file too there can be a directive #include, that substituted for after including of file containing this directive. The directive #include is widely used for plugging in the program of the so-called heading files, containing the prototypes of library functions, and most programs on SI are begun with this directive.