/in/ex5.c:1:10: error: #include expects "FILENAME" or <FILENAME>
 #include ...
          ^~~
/in/ex5.c: In function 'main':
/in/ex5.c:9:2: error: implicit declaration of function 'scanf' [-Werror=implicit-function-declaration]
  scanf("%d\n", &n);
  ^~~~~
/in/ex5.c:9:2: error: incompatible implicit declaration of built-in function 'scanf' [-Werror]
/in/ex5.c:9:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/ex5.c:12:19: error: implicit declaration of function 'malloc' [-Werror=implicit-function-declaration]
   arr[i] = (char*)malloc(MAX_LENGTH * sizeof(char));
                   ^~~~~~
/in/ex5.c:12:19: error: incompatible implicit declaration of built-in function 'malloc' [-Werror]
/in/ex5.c:12:19: note: include '<stdlib.h>' or provide a declaration of 'malloc'
/in/ex5.c:13:3: error: implicit declaration of function 'fgets' [-Werror=implicit-function-declaration]
   fgets(arr[i], MAX_LENGTH, stdin);
   ^~~~~
/in/ex5.c:13:29: error: 'stdin' undeclared (first use in this function)
   fgets(arr[i], MAX_LENGTH, stdin);
                             ^~~~~
/in/ex5.c:13:29: note: each undeclared identifier is reported only once for each function it appears in
/in/ex5.c:19:8: error: implicit declaration of function 'strcmp' [-Werror=implicit-function-declaration]
    if (strcmp(arr[j], arr[i]) < 0)
        ^~~~~~
/in/ex5.c:29:3: error: implicit declaration of function 'printf' [-Werror=implicit-function-declaration]
   printf("%s", arr[i]);
   ^~~~~~
/in/ex5.c:29:3: error: incompatible implicit declaration of built-in function 'printf' [-Werror]
/in/ex5.c:29:3: note: include '<stdio.h>' or provide a declaration of 'printf'
cc1: all warnings being treated as errors