php 数组中在最后一个位置插入元素

$str=Array
(
[0] =>111
[1] => 222
[2] => 33
[3] => 44
[4] =>55
[5] => 666
)
想在数组中再手动添加一个元素在最后的位置
效果是这样的：
Array
(
[0] =>111
[1] => 222
[2] => 33
[3] => 44
[4] =>55
[5] => 666
[6] => 777
)

相关了解……