Hi, guys I just begin learning how to program in Xcode 4.3. And I am attending class of C program in university, so I use Xcode Command Line to run some simple C programs. My operation is as follows: Run Xcode 4.3 - Create a new Xcode project - Application (under 'Mac OS X' menu) - Command Line Tool. Then I copied content of *.c to Main.c in the new project, and then build and run in Main.c. My question is, when I add a new .c file to this project, I can not build Main.c successfully. what should I do to add new .c files associated with Main.c into the project? Please help me, thank you very much!