/in/foo.c: In function 'copyVowels':
/in/foo.c:5:21: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
    5 |     for (i = 0; i < strlen(input); i++) {
      |                     ^~~~~~
/in/foo.c:2:1: note: include '<string.h>' or provide a declaration of 'strlen'
    1 | #include <stdio.h>
  +++ |+#include <string.h>
    2 | 
/in/foo.c:5:21: warning: incompatible implicit declaration of built-in function 'strlen' [-Wbuiltin-declaration-mismatch]
    5 |     for (i = 0; i < strlen(input); i++) {
      |                     ^~~~~~
/in/foo.c:5:21: note: include '<string.h>' or provide a declaration of 'strlen'