Preprocessor part 1

• The C preprocessor is a program that processes our source program before it is passed to the compiler.
• preprocessor is a separate program which transforms C source code containing preprocessor directives into source code with the directives removed.
• The preprocessor is implemented as an integral part of an Standard C compiler.
• gcc -E filename will show the preprocessed file.
• Preprocessor commands are known as directives.
• Preprocessor works on a line by line basis.
• The preprocessor doesn't know about the scope rules of C. Preprocessor directives like #define take effect as soon as they are seen and remain in effect until the end of the file that contains them

Preprocessor Directives:

• The preprocessor commands are called as directives.
• Each of these preprocessor directives begin with a # symbol.
• The directives can be placed anywhere in a program but they are most often placed at the beginning of a program.
• The preprocessor directives are classified in to 4 major categories
  
  
  1. Macro Expansion(#define)
  2. File Inclusion(#include)
  3. Conditional Compilation
  4. Miscellaneous directives
• The 2 most frequently used features are #include,to include the contents of a file during compilation and #define ,to replace a token by an arbitrary sequence of characters.