If you want to do something or you are doing something, and then you decide not to do or decide to stop doing for some reason, you would say 不干了。 If you want to go somewhere or you are on your way to somewhere, and then you decide not to go there, you would say 不去了。 likewise, if i am eating something, for some reason i decide to stop eating, i would say 不吃了 I know you're learning chinese now, i don't want to hear you say 不学了，太难了。 哈哈

in this sentence ,it 's an Chinese oral express. 辞职 and 不干了,they got same meaning . 辞职 means quit ; 不干了means not to do or doing anything anymore . they both infer to STOP DOING THE WORK /QUIT (the work). in written Chinese, we just say 他就辞职了，他就不干了。

他辞职，老板可能不同意；他辞职不干了，就把辞职的结果也说明白了，老板同意不同意，他都不干了。不干了：放弃，give up.

不干了=stop to do sth （辞职=不干了，不做某事基本上都可以说是不干了