Crystal (1987) suggests that code switching occurs when individual who is bilingualism alternates between two languages during his/her speech with another bilingual person.
There are kinds of code switching as suggested by some sociolinguists:
Blom and Gumperz (1972):
Situational Code Switching
It occurs when the language change according to the situational in which the conversations find themselves; It can be found in the use of speech level in languages which have speeches levels....