understanding C macros when they are inside some conditional statements like switch/if/esle

Question

As you can see from the code that i have a switch statement and here inside each separate switch branch I'm defining a macro. and in later part of the code, based upon these macros I'm printing some ouput to terminal. So in this scenario what would be the output of the below code?

    #include <stdio.h>
    int main() 
    {
        // k integer to hold user input
        int k;
        
        scanf("%d",&k); // capture input here

        switch(k)
        {
            case 1 :
            #define first_case
            break;
            case 2 :
             #define second_case
            break;
            case 3 :    
             #define third_case
            break;
            case 4 : 
            #define fourth_case
            break;
        }
        
    
 #ifdef first_case
        printf(" first_case\n");
  #endif

  #ifdef second_case
        printf(" second_case\n");
  #endif
        
  #ifdef third_case
        printf(" third_case\n");
 #endif

   #ifdef fourth_case
        printf(" fourth_case\n");
 #endif
    
    }

Answer 1

Macros (#define MACRO ...) are processed by the C preprocessor before the actuel compile process takes place.

So the compiler only "sees" this once the file has been preprocessed:

int main()
{
  // your code goes here
  int k = 0;

  scanf("%d", &k);
  switch (k)
  {
  case 1:
    break;
  case 2:
    break;
  case 3:
    break;
  case 4:
    break;
  }

  printf("typed first_case\n");
  printf("typed second_case\n");
  printf("typed third_case\n");
  printf("typed fourth_case\n");
}

You could write your program like this, and the outcome would be exactly the same:

#define first_case
#define second_case
#define third_case
#define fourth_case

/* Find the longest line among the giving inputs and print it */

#include <stdio.h>
int main()
{
  // your code goes here
  int k = 0;

  scanf("%d", &k);
  switch (k)
  {
  case 1:
    printf("case 1\n");
    break;
  case 2:
    break;
  case 3:
    break;
  case 4:
    break;
  }


#ifdef first_case
  printf("typed first_case\n");
#endif
#ifdef second_case
  printf("typed second_case\n");
#endif

#ifdef third_case
  printf("typed third_case\n");
#endif
#ifdef fourth_case
  printf("typed fourth_case\n");
#endif

}