CPP program to get exactely - yes (y) or no(n) option

 Program to get options (Y/y) for  yes or  ( N/n) for no. Neither will be accepted other  than those.

#include <iostream>
#include <string>

using std::string;
using std::cin;
using std::cout;
using std::endl;

char charExtract(string str)
{
    string::iterator istr;

    char ch;

    istr = str.begin();
    ch = *istr;

    if(str.length() == 1)
        return ch;
    else
        return 0;
}

bool yesno()
{
    string str;
    char ch;

    int i;

    while(1)
    {
        cout << "Enter y(yes) or n(no) : ";

        getline(cin, str);

        if(str.length() == 0 )
            continue;
        else
        {
             ch = charExtract(str);

            if(ch == 'Y' || ch == 'y')
            {
                return true;
            }

            else if(ch == 'N' || ch == 'n')
            {
                return false;
            }

            else
            {
                cout << "\nEnter only Y(yes) or N(No)"  << endl;
            }
        }
    }
}

int main()
{

    bool yn = yesno();

    if(yn == true)
    {
        cout << "true" << endl;
    }
    else if( yn == false)
    {
        cout << "false" << endl;
    }


    return 0;
}
/*
output :-
-------------
[rahul@C-Client Release]$ ./yes-no
Enter y(yes) or n(no) : YES

Enter only Y(yes) or N(No)
Enter y(yes) or n(no) : NO

Enter only Y(yes) or N(No)
Enter y(yes) or n(no) : Nu

Enter only Y(yes) or N(No)
Enter y(yes) or n(no) : 123

Enter only Y(yes) or N(No)
Enter y(yes) or n(no) : 1

Enter only Y(yes) or N(No)
Enter y(yes) or n(no) : 0

Enter only Y(yes) or N(No)
Enter y(yes) or n(no) : Y
true
[rahul@C-Client Release]$ ./yes-no
Enter y(yes) or n(no) : y
true
[rahul@C-Client Release]$ ./yes-no
Enter y(yes) or n(no) : N
false
[rahul@C-Client Release]$ ./yes-no
Enter y(yes) or n(no) : n
false
[rahul@C-Client Release]$
*/