is main function in C/C++ user defined function or predefined function?plz answer for this with explanation.

pre-defined. Main is the entry point to your application that the compiler expects to see when running your application but in there you can make calls to your user defined functions.

@Poster
Your question is a bit vague. Kobo has already answered the better part of it.
Here's what's left. Some compilers (e.g devC++) pre-declare the main function when the user creates a new C++ project. In others, the actual declaration of the main function is done by the user.
The user initiated declaration is usually better tailored to the peculiarities of ones project.

thank u for giving me the answer.