What is happen?

Question

https://code.sololearn.com/cxpgMEMKo5DY/?ref=app

Answer 1

2 things are wrong.
In c++ you need to declare a function before you can use it. It is enough to just declare a prototype. Put this before your main function:
int stonetolb(int);
And maybe you already saw what I changed in the function. Your function has no return type. You need to return an integer and therefore need to declare it as int stonetolb, not void stonetolb.

Answer 2

If you don't want to declare a function prototype, then place the function before your main function, e.g.

void func() { //do something }

int main() { }