We can open stdin file using operating system. Basically it touched with keyboard.It comes from an I/O redirected file. Some functions used by stdin are given below: getchar(): Use to get character from stdin gets(): Use to get a string from stdin scanf(): Use to performs a formatted read from stdin stdout�s output goes to a redirected file.Program to use the screen by opening a file called con. Some functions used by stdin are given below: printf(): Use to performs a formatted write to stdout putchar(): use to writes a character to stdout puts(): Writes the buffer to stdout vprintf(): Performs a formatted write to stdout. The output is pointed to by a parameter-list pointer.