Look at your code:
static int Getanswer(char answer)
{
string result;
...
return result;
}
Your method is defined as returning an integer, but you are explicitly telling it to return a string. You can't do that: change the definition of the method to return a string and that'll fix it:
static string Getanswer(char answer)
{
string result;
...
return result;
}