is a text-substitution tool that modifies the source code before the compilation takes place. This modification is done according to the preprocessor directives that are included in the source files. The directives are easily distinguished from normal programming code in that they all start with a hash sign (#
). They must always appear as the first non-whitespace character on a line, and they do not end with a semicolon. The following table shows the preprocessor directives
available in C++ along with their functions.