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C - Conditional Compilation

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Conditional Compilation

  • It is possible to control preprocessing itself with conditional statements that are evaluated during preprocessing. This provides a way to code selectively, depending on the value of conditions evaluated during compilation.
  • The conditional statements are : #if, #elif, #else, #endif, #ifdef, #ifndef, and #defined
  • The #if line evaluates a constant integer expression. If the expression is non-zero, subsequent lines are included until an #endif or #elif or #else is encountered.
  • The #ifdef and #ifndef are specialized forms that test whether a name is defined.