I ain't gonna stop by MacDnold's, I wanna sth. decent 2day.

Gotta, Wanna, Gonna, are used in written English to represent the words  when they are pronounced > informally. They are not slang.

gotta = got to

wanna =want to

gonna=going to

Here in Ontario Canada , I can report that everyone I know, even highly educated people, use these forms normally. People in business meetings, professors giving lectures,... everyone. Sometimes people are being slow, clear, and deliberate, in which case they will pronounce the full phrase, which does sound more formal by comparison.

Me? I don't remember when was the last time I spoke: I am going to ... ... 

Ain't  是个百搭字=am not, are not, is not, have not, have no 

Ain't no sunshine 歌词: 为了rhym也是拼了啊,  什么语法不语法都是爆弱了, 

Ain't no不是否定之否定吗?

Ain't no sunshine= there is no sunshine,

Ain't No Sunshine

Bill Withers

Ain't no sunshine when she's gone
It's not warm when she's away
Ain't no sunshine when she's gone
And she's always gone too long
Anytime she goes away

Wonder this time where she's gone
Wonder if she's gone to stay
Ain't no sunshine when she's gone
And this house just ain't no home
Anytime she goes away

And I know, I know, I know, I know
I know, I know, I know, I know, I know
I know, I know, I know, I know, I know