Defference Between #if #else #endif And Regular if, else

Question

As the title states, I was wondering what are the differences between using

#if
   DoWork();
#else
   DoAnotherWork();
#endif

and

if (debug)
   DoWork();
else
   DoAnotherWork();

Answer 1

if (debug)
    DoWork();
else
    DoAnotherWork();

The above code will be compiled and the condition will be checked at runtime.

#if
    DoWork();
#else
    DoAnotherWork();
#endif

These statements will be checked at compile time.

So if #if condition is true, DoWork(); will be compiled and otherwise DoAnotherWork(); will be compiled. Where as in the previous example all code including the if statement will be compiled.

Please read this on Preprocessor Directives

Preprocessor Directives

Answer 2

First is Preprocessor Directive and second Logical statement.