Code-switching in English.

I heard the sentence in class "One found the need to learn code-switching the most difficult."

Code-switching is the switching between SSE(Standard Singapore English) and SCE(Singapore Colloquial English) in a paticular person.
SCE may also be called singlish.

I think code-switching is important because some people will know more SSE than others. For example, you should use SCE when talking to the man in a hawker centre. But you should use SSE when talking to the principle because it's more polite to do that.