WinMerge is a program that compares textbetween two different files, and determines the differences between them. It is useful to compare different versions of a document, and identify differences.
While WinMerge can be used to compare any type of document is aimed primarily at code files with any programming language. Recognizes the syntax of several languages in different colors and highlights keywords, functions, loops, etc.. It has several editing tools, also with line numbering, word-wrap, etc..
When comparing two codes with color highlights the lines that are in a file and not the other and vice versa. Pressing a button may be seeing exactly the portions that are different between the two lines. You can mix together or parts of both codes.
You can filter the text to compare to exclude words or phrases. The filter supports regular expressions.