Question

I am a bit confused about the following if_even function. How is the return type FLAGS? This seems strange – isn’t an enum just a list of multiple integers to be used like #define‘s ?

enum flag_o_e {EVEN, ODD};
enum flag_o_e test1;
typedef enum flag_o_e FLAGS;

FLAGS if_even(int n);

main()
{
  int x;
  FLAGS test2; 

  printf("input an integer: ");  scanf("%d", &x);
  test2 =  if_even(x); 
  if (test2 == EVEN)
    printf("test succeeded (%d is even)\n", x);
  else
    printf("test failed (%d is odd)\n", x);system("pause");
}

FLAGS if_even(int  n)
{
  if (n%2)
    return ODD;
  else
    return EVEN;

   }

I appreciate any tips or advice.

Answer 1

Yes the enum declared at declared at the very top enum flag_o_e {EVEN, ODD}; is just the same as doing

#define EVEN 0
#define ODD 1
typedef int flag_o_e;

Then there is a further typedef to use FLAGS in place of flag_o_e so its essentially:

#define EVEN 0
#define ODD 1
typedef int FLAGS;

So when if_even() executes return EVEN; its actually returning an int, and similarly the comparison of the result if (test2 == EVEN) is comparing the result (which is really an int) with EVEN, which is also an int.

typedef’s can get a little confusing, but its just a technique to rename a type (such as int, or ‘struct foo’) to something more readable and contextual.