Well I know how I would ordinarily do it with strings..

Code:

---

string chstrswithf(string a)
{
        int temp_pos = 0;
	while(a[temp_pos] != '\0')
	{
		if(a[temp_pos] == 's')
			a[temp_pos] = 'f';
		a++;
	}
	return a;
}

---

BUT Lite-C doesn't seem to support indexing a string..

It's late though, so I hope you get this figured out.. Perhaps I will look at it again when I get up.

Good luck,