Pre ++ and post ++ overloads

To distinguish between the prefix and postfix versions of the ++ operator, C++ adopted the convention of letting operator++() be the prefix version and operator++(int) be the suffix version;`

iterator& operator++() // for ++it
{
pt = pt->p_next;
return *this;
}
iterator operator++(int) // for it++
{
iterator tmp = *this;
pt = pt->p_next;
return tmp;
}`

Reference material ：
《C++ Primer》