Why do I get this warning?

Question

Why do I get this warning saying that I implicitly declared tolower()?
(Ignore the other warnings)
Thank you🤗

https://code.sololearn.com/cUwhHRywUtYv/?ref=app

Answer 1

The tolower() function is defined in <ctype.h> header. You have not included it. Include it to remove the warning
#include <ctype.h>

Answer 2

XXX and Aditya thank you, I got it