Please tell me what upper_bound and lower_bound are in the C++ Standard Library and how they work.

Answer 1, authority 100%

Well, for example, you have a ordered (important!) sequence

1 2 3 4 4 4 5 5 5 5 5 6 7

When looking for upper_bound for a value of 5 this there will be an iterator (a pointer if the concept of an iterator is new to you) to the value 6 – the first larger value .

Accordingly, lower_bound will point to the first not less value – the first 5.

For example code

int main (int argc, const char * argv [])
{
  int a [20] = {1,2,3,4,5,6,7,7,7,7,8,9,9,11,11,12,16,20,20,20,20};
  for (int * p = lower_bound (a, a + 20,10);
    p! = upper_bound (a, a + 20.20); ++ p)
    cout & lt; & lt; * p & lt; & lt; "";
  cout & lt; & lt; endl;
}

gives

11 11 12 16 20 20 20 20