Issue on a do-while form in Strings

Ok, i'm a student in his first experiences with programmaing so be kind ;) this is the correct code to print "n" times a string on screen...

#include <stdio.h>
 #include <string.h>
 
 #define MAX 80+1+1 /* 80+\n+ */
 
 int main(void)
 {
   char message[MAX];
   int i, n;
 
   /* input phase */
   printf("Input message: ");
   i = 0;
   do {
     scanf("%c", &message[i]);
   } while (message[i++] != '\n');
   message[i] = '';
 
   printf("Number of repetitions: ");
   scanf("%d", &n);
 
   /* output phase */
   for (i=0; i<n; i++) {
     printf("%s", message);
   }
 
   return 0;
 }
 

why in the do-while form he needs to check if message[i++] != '\n' and not just message[i] != '\n'??

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