How can two alternating characters be output efficiently or without a loop?

Question

It's a bit tricky to explain the question, but suppose two alternating chars must be shown:

for(int n=0; n<20; n++)
{
    cout<<(n%2==0 ? 'X' : 'Y');
}

Is there a one-liner or more efficient way to accomplish the task above? (i.e. using something like <iomanip>'s setfill())?

Answer 1

I think I'd keep it simple:

static const char s[] ="XY";

for (int n=0; n<20; n++)
    std::cout << s[n&1];

The other obvious possibility would be to just write out two characters at a time:

for (int n=0; n<total_length/2; n++)
    std::cout << "XY";

Answer 2

If I work with strings and concise code matters a bit more than performance (like you have in Python), then I might write just this:

 static const std::string pattern = "XY";
 std::cout << pattern * n; //repeat pattern n times!

And to support this, I would add this functionality in my string library:

std::string operator * (std::string const & s, size_t n)
{
   std::string result;
   while(n--) result += s;
   return result;
}

One you have this functionality, you can use it elsewhere also:

std::cout << std::string("foo") * 100; //repeat "foo" 100 times!

And if you have user-defined string literal, say _s, then just write this:

std::cout << "foo"_s * 15;  //too concise!!

std::cout << "XY"_s * n;  //you can use this in your case!

Online demo.

Cool, isn't it?