triple is defined correctly, but after main, which calls it. Submit as-is and read the error – it’s the
“implicit declaration” error from the previous lesson, except this time nothing is missing an #include; the
function simply hasn’t been declared yet at the point it’s called.
Fix it by adding a forward declaration (a prototype, int triple(int n);, with no body) above main. This is a
one-file rehearsal of exactly what a header file does across files: it lets code that comes first refer to code
defined later, anywhere in the project.