Hello world!
Hello again!
element3
element4
element5_long_element5
element3 found at position 2
After erase (end,end):
Hello world!
Hello again!
element3
element4
element5_long_element5
After erase (2,2):
Hello world!
Hello again!
element5_long_element5
After pop_back():
Hello world!
Hello again!
element3
element4
After insert(1,1,3):
Hello world!
Hello again!
element3
element4
Hello again!
element3
element4
element5_long_element5