what the wrong in function check

int main ()
	case 4:
	{
			
			bool c=a.check();
			if (c==true)
			{cout <<"the number is even "<<endl;}
			else
			{cout <<"the number is odd "<<endl;}
		break;
		}

bool check ( )
{
    cout << "Enter big integer number :";
        string s;
        getline(cin,s);
    string::const_reverse_iterator s1 = s.rbegin();
    if (*s1 %2==0)
    {return true;}
    else
    {return false;}
}