#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

int main() {
   char *s1 = "abc";
   char *s2 = "def";
   int i;

   for (i=1; i<=10; i++) {
     char *sum = (char*)malloc(255);
     sum[0] = '\0';
     strcat(sum, s1);
     strcat(sum, s2);
     printf("%s\n", sum);
     free(sum);
   }
}