The main tool you use to write your code is the Xcode text editor. This advanced text editor provides several convenient features:
Header-file lookup. By Command–double-clicking a symbol, you can view the header file that declares the symbol.
API reference lookup. By Option–double-clicking a symbol, you get access to API reference that provides information about the symbol’s usage.
Code completion. As you type code, you can have the editor help out by inserting text for you that completes the name of the symbol Xcode thinks you’re going to enter. Xcode does this in an unobtrusive and overridable manner.
Code folding. With code folding, you can collapse code that you’re not working on and display only the code that requires your attention.