some features of PREPROCESSOR in c and C++

[Xpert]

The preprocessor performs preliminary operations on C and C++ files before they are passed to the compiler. You can use the preprocessor for

• File inclusion, in which the file being preprocessed incorporates the contents of another file, exactly as if the included file’s text were actually part of the including file;
  
• Macro substitution, in which one sequence of text is replaced by another;
  
• Conditional compilation, in which parts of the source file’s code can be eliminated at compile time under certain circumstances.