[C and pointer] # if 0 # end if

1. The role of "# if 0/# if 1... # endif" is 1) the code defined in the code is the code of some debugging versions. At this time, the code is completely ignored by the compiler. If you want the code to take effect, you only need to change # if 0 to # if 1 2) # if 0 is also used as a comment. if the program you want to comment on is very long, at this time, # if 0 is the best, so that no mistakes are made # if 1 can make the variables in it a local variable. 3) This structure indicates the code you wrote earlier. If you don't want to delete it, you can use this method, which is more convenient than annotation. 2. Example [html] # include <iostream> int main (void) {int a = 0; # if 0 a = 1; # endif printf ("% d \ n ", a); return 0 ;}