Currently I am developing a couple of C programs on my mac using Xcode. There however is 1 problem. My study requires me to use some sort of input field through the coding.
It sounds like you need to check argc in the program as RageD points out, otherwise when launching the program with insufficient arguments will cause problems.
gcc is the c compiler - it produces an executable. When you hit 'Run' in Xcode it compiles your program and then runs the executable file created. The executable created is named the same as your Xcode project name.
To run the program you built in Xcode from the command line:
The result will look something similar to the snippet below (for my 'MyCommandLineApp' project):
$ /Users/pliskin/Library/Developer/Xcode/DerivedData/MyCommandLineApp-hbpuxhguakaagvdlpdmqczucadim/Build/Products/Debug/MyCommandLineApp argument1 argument2