(C and pointers) #if 0/#if 1 ... #end If_c language

I. The role of "#if 0/#if 1 ... #endif"

1 code is defined in a number of debug version codes, this time the code is completely ignored by the compiler. If you want code to take effect, just change #if 0 to #if 1.

2 #if 0 There is also an important use for annotations, if you want to annotate the program is very long, this time #if 0 is the best, guaranteed not to make mistakes

#if 1 allows the variable to become a local variable.

3 This structure means that your previously written code, now used, and do not want to delete, use this method, more convenient than the annotation.

two. Examples

Copy Code code as follows:

#include <iostream>
int main (void)
{
int a = 0;
#if 0
A = 1;
#endif

printf ("%d\n", a);
return 0;
}