What is the importance of .pch file and what is the significance of"#ifdef OBJC"?
Also, where do we define parameters like "#ifdef IS_PRODUCTION" which are checked in .pch file.
.pch is a Pre-Compile Header.
In the C and C++ programming languages, a header file is a file whose text may be automatically included in another source file by the C preprocessor, usually specified by the use of compiler directives in the source file.
#ifdef OBJC lets the compiler know that the code is Objective-C.
#ifdef IS_PRODUCTION is something you have defined on your own, a directive telling the compiler to do something only if this is defined, most-likely something for a PRODUCTION build.