import is a feature provided by the GCC compiler, which is what Xcode uses when you’re compiling Objective- C, C, and C++ programs. #import guarantees that a header file will be included only once, no matter how many times the #import directive is actually seen for that file.
NOTE
In C, programmers typically use a scheme based on the #ifdef directive to avoid the situation where one file includes a second file, which then, recursively, includes the first.
In Objective- C, programmers use #import to accomplish the same thing.
So import equals to ifndef plus include.
