What does such an expression mean?

Question

C++ / C#

I came across this entry:

int main()
{
  std::list<int> x = {1, 2, 2, 3, 3, 2, 1, 1, 2};
 
  std::cout << "contents before:";
  for (auto val : x)
    std::cout << ' ' << val;
  std::cout << '\n';

}

Can't figure out the meaning:

for (auto val : x)

And shouldn't for have such a pattern?
for (; ;)

Answer 1

Discover C++11. This is a new language standard that has improved syntax.
for (auto val : x) is a loop through the collection x, each element of the collection will be copied to the x variable.