what do these operators mean?

Question

I saw this code:
int a;
a=5>4?3>8?40:20:30;
cout<<a;

and the result was 20.

i don't know the operators "?" ":", and what do they mean, and what they do in that contest.
thanks.

Answer 1

a>b?c:d means:

if(a > b)
{
return c;
}
else
{
return d;
}

5>4?9>8?40:20:30 means

if(5 >4)
{
if(9>8)
{
return 40;
}
else
{
return 20;
}
}
else
{
return 30;
}

Answer 2

it is a puzzle, so unclarity is the idea.