Comments C++ C++ language Basic Concepts Comments serve as a sort of in-code documentation. When inserted into a program, they are effectively ignored by the compiler; they are solely intended to be used as notes by the humans that read source code. Although specific documentation is not part of the C++ standard, several utilities exist that parse comments with different documentation formats.

Syntax /* comment */ (1) comment (2) 1) Often known as “C-style” or “multi-line” comments. 2) Often known as “C++-style” or “single-line” comments. All comments are removed from the program at translation phase 3 by replacing each comment with a single whitespace character. C-style C-style comments are usually used to comment large blocks of text, however, they can be used to comment single lines. To insert a C-style comment, simply surround text with /* and */; this will cause the contents of the comment to be ignored by the compiler. Although it is not part of the C++ standard, / and */ are often used to indicate documentation blocks; this is legal because the second asterisk is simply treated as part of the comment. C-style comments cannot be nested. C++-style C++-style comments are usually used to comment single lines, however, multiple C++-style comments can be placed together to form multi-line comments. C++-style comments tell the compiler to ignore all content between and a new line. Notes Because comments are removed before the preprocessor stage, a macro cannot be used to form a comment and an unterminated C-style comment doesn't spill over from an #include'd file. Besides commenting out, other mechanisms used for source code exclusion are #if 0 std::cout « “this will not be executed or even compiled\n”; #endif and if (false) { std::cout « “this will not be executed\n”; } Example Run this code #include <iostream> /* C-style comments can contain multiple lines */ /* or just one */ /** * you can insert any *, but * you can't make comments nested */ C++-style comments can comment one line or, they can be strung together int main() { comments are removed before preprocessing, so ABC is “1”, not “12134”, and “1 hello world” will be printed #define ABC 12134 std::cout « ABC « “ hello world\n”; The below code won't be run return 1; The below code will be run return 0; } Output: 1 hello world