This is just a condensed one-line if statement.
if(a>b)win+=3;
This can be rewritten as
if (a>b)
{
    win = win + 3;
}
The following line
v.push_back(b-a)
Calculates the difference of b - a then uses push_back to add it to the end of the vector v.
3
solved Don’t understand what this lines do [closed]