Conio.h is expanded as console input output header file 
conio.h is a C header file used in old MS-DOS compilers to create text user interfaces . 
eg. clearscr() ,getch() are from conio.h 
This is type of opening files before we use these function.
If we use these function  without importing header files , sometimes error would be displayed, if u try compiling it.
Conio.h is a C header file used mostly by MS-DOS compilers to provide console input/output.
there are all function in conio.h. 
Member functionskbhit - Determines if a keyboard key was pressed.getch - Reads a character directly from the console without buffer, and without echo.getche - Reads a character directly from the console without buffer, but with echo.ungetch - Puts the character c back into the keyboard buffers.cgets - Reads a string directly from the console.cscanf - Reads formatted values directly from the console.putch - Writes a character directly to the console.cputs - Writes a string directly to the console.cprintf - Formats values and writes them directly to the console.clrscr - Clears the screen.