This is how you read (string) from the standard input: cin >> answer;
Then you can compare it against the expected results: if (answer == "a")
When you declared your variables, it should end with a semicolon, which you were missing. Instead you had another comma after d.
char a, b, c, d;
Last but not least, when you check for the values b, c and d, you should do it in a series of if-else otherwise multiple results will be displayed.
Here's the whole code fixed:
#include <iostream>
#include <string>
using namespace std;
int main ()
{
cout << "Do You Want To Play 80 Days Around The World?";
cout << "\n B) Yes"; // making the question
cout << "\n C) No";
cout << "\n D) Maybe";
cout << "\n";
string answer;
cin >> answer;
if (answer == "b")
{
cout << "Yay";
}
else if (answer == "c")
{
cout << "Aww";
}
else
{
cout << "well...";
}
return 0;
}