Comment (computer programming)

In computer programming, a comment is a programmer-readable explanation or annotation in the source code of a computer program. They are added with the purpose of making the source code easier for humans to understand, and are generally ignored by compilers and interpreters. The syntax of comments in various programming languages varies considerably. Comments are sometimes also processed in various ways to generate documentation external to the source code itself by documentation generators, or used for integration with source code management systems and other kinds of external programming tools. The flexibility provided by comments allows for a wide degree of variability, but formal conventions for their use are commonly part of programming style guides. Comments are generally formatted as either block comments (also called prologue comments or stream comments) or line comments (also called inline comments). Block comments delimit a region of source code which may span multiple lines or a part of a single line. This region is specified with a start delimiter and an end delimiter. Some programming languages (such as MATLAB) allow block comments to be recursively nested inside one another, but others (such as Java) do not. Line comments either start with a comment delimiter and continue until the end of the line, or in some cases, start at a specific column (character line offset) in the source code, and continue until the end of the line. Some programming languages employ both block and line comments with different comment delimiters. For example, C++ has block comments delimited by /* and */ that can span multiple lines and line comments delimited by //. Other languages support only one type of comment. For example, Ada comments are line comments: they start with -- and continue to the end of the line. How best to make use of comments is subject to dispute; different commentators have offered varied and sometimes opposing viewpoints. There are many different ways of writing comments and many commentators offer conflicting advice.