Merging projects

Ok, so a friend and I are working on a huge project. Last night we both got tons of work done but didnt know the other was working on it. Is there any program out there that merges porject files and tells you whats diffrent? Like you got a file called File.cs and the namespaces are the same but there are 2 more functions to it? So it merges them

Lookup WinMerge or BeyondCompare. Both are free and will take 2 files, compare them, show the line by line differences, and let you select which changes to keep.