The root cause of this error is a stack overflow. The function `fib`
calls itself recursively without a base case, causing the stack to
fill up with too many function calls and resulting in a stack
overflow.

A fix for this would be to add a base case that stops the recursion,
for example:

```
int fib(int n) {
  if (n <= 1) {
    return n;
  }
  return fib(n-1) + fib(n-2);
}
```

This way, the recursion will stop when `n` is 0 or 1 and prevent a
stack overflow.
