Is there any difference in the syntax of writing simple c programs in Xcode ?, Is there any difference in the syntax of writing simple c programs in Xcode ?

You should learn using Objective C or Swift.

Check the iBooks Store.

Here's iBooks link and is free: Using Swift with Cocoa and Objective-C

conio.h is a C header file used mostly by MS-DOS compilers to provide console input/output. It is not part of the C standard library or ISO C, nor is it defined by POSIX.

This header declares several useful library functions for performing "console input and output" from a program. Most C compilers that target DOS, Windows 3.x, Phar Lap, DOSX, OS/2, or Win32 have this header and supply the associated library functions in the default C library. Most C compilers that target UNIX and Linux [this includes OSX] do not have this header and do not supply the library functions. Some embedded systems use a conio-compatible library.

- http://en.wikipedia.org/wiki/Conio.h

Languages like C and C++ have relatively small standard libraries (compared to e.g. Java) and instead rely on OS libraries or non-standard libraries supplied by certain compilers, the MS-DOS conio.h is an example of this.

Some versions of Turbo-C (see http://en.wikipedia.org/wiki/Borland_Turbo_C) appear to predate modern standard C (ANSI C-89 / C-99 / C-11)

so you might run into issue with C syntax and libraries supported by Turbo-C deviating from modern C.