You also have at your disposal a large collection of built-in C library files. A library file is a centrally located collection of C functions, along with a .h file that you can include in order to make those functions available to your code.
For example, suppose you want to round a float up to the next highest integer. The way to do this is to call some variety of the
ceil function. You can read the
ceil man page in Xcode, or by typing
man ceil in the Terminal. The documentation tells you what
#include to use to incorporate the correct header and also shows you the function declarations and tells you what those functions do. A small pure C program might thus look like this:
#include <math.h> float f = 4.5; int i = ceilf(f); // now i is 5
In your iOS programs, math.h is included for you as part of the massive UIKit
#import, so there’s no need to include it again. But some library functions might require an explicit
The standard library is discussed in K&R Appendix B. But the modern standard library has evolved since K&R; it is a superset of K&R’s library. The
ceil function, for example, is listed in K&R appendix B, but the
ceilf function is not. Similarly, if you wanted to generate a random number (which is likely if you’re writing a game program that needs to incorporate some unpredictable behavior), you probably wouldn’t use the
rand function listed in K&R; you’d use the
random function, which supersedes it.