Standard C (C89 and C99 are the official standards) does not allow to define functions inside functions (known as nestedfunctions). However, some compilers, such as the free GCC allow nested functions as a language extension.
That depends on where you define them. Arrays defined inside functions are declared on the stack (like other variables defined in functions). Arrays defined outside of any function, or using the static keyword inside a function are allocated in the static data area of the program. Other arrays may be allocated using malloc() (or "new" in C++); these are allocated on the heap.
The main function in C is user-defined. Built-in functions are simply those that do not require a library to be included, but every program must provide a user-defined point of entry; it cannot be built-in. Indeed, most functions in C are user-defined; the built-in functions are mostly operators rather than functions although most do behave like functions. The standard library functions are not built-in either; they all require the inclusion of the appropriate standard library header.
to create user defined functions the user defined data is needed nd its useful to the programmer to create its own data.
Ideally, functions should only be declared in a header and defined in a translation unit (source file) that includes the header. However, trivial functions are often defined in a header as they are usually good candidates for inline expansion, but you must remember to declare the function inline. Often it is better to forward declare inline functions so that maintainers are not distracted by the implementation details which can be placed towards the end of the header, out of the way. However, a definition is also a declaration, so forward declaring an inline function is not a requirement unless there is a cyclic dependency issue where a forward declaration is necessary to break the cycle.
No. There are no built-in functions in C, there are only built-in types and built-in operators for those types. All functions are user-defined, including those defined by the C standard library. There are no user-defined operators in C, but you can implement operators as named functions if required. A header file (*.h file) typically contains a group of related user-defined function and/or user-defined type declarations which can be included in any source file that requires them. Every user-defined function or user-defined type name used by a program must have one (and only one) definition, usually contained in a corresponding source file (*.c file) or library file (*.lib file). Built-in types and their corresponding operators do not require a header file since they are part of the language itself (hence they are built-in).
That depends on where you define them. Arrays defined inside functions are declared on the stack (like other variables defined in functions). Arrays defined outside of any function, or using the static keyword inside a function are allocated in the static data area of the program. Other arrays may be allocated using malloc() (or "new" in C++); these are allocated on the heap.
There are no 'sections' in C source, you can define functions anywhere, except inside another function or variable/type definition.
The C++ standard library contains all the pre-defined functions.
No, all functions must be defined outside of C structures. However, all functions in C have a type (the return type) and an identity (an address), so you can define function pointers as members of a structure to achieve the same end.
Predefined functions are functions that have been written and we can use them in our C++ statements. But we must know how to use each of these predefined functions.
The main function in C is user-defined. Built-in functions are simply those that do not require a library to be included, but every program must provide a user-defined point of entry; it cannot be built-in. Indeed, most functions in C are user-defined; the built-in functions are mostly operators rather than functions although most do behave like functions. The standard library functions are not built-in either; they all require the inclusion of the appropriate standard library header.
Header File in C/C++ are the files which contains the definition of the pre-defined functions, data-types & constants, etc. By adding the header file you reduce your job of defining the same functions which are defined earlier by someone else & you can use those functions/data-types easily.
There are many advantages to C sharp programming like: Not having to define the Headers (.h), Classes can be defined within classes, classes and functions can be defined in random order unlike C and C++, Classes and functions don't need to be declared in the program.
to create user defined functions the user defined data is needed nd its useful to the programmer to create its own data.
C++ built-in functions are those functions that are provided for you as part of the language itself, and includes all of the C standard library functions (all of which were inherited from C) and is expanded upon by the C++ standard template library. C++ implementors may provide additional functions that are platform-specific, however these are not considered built-in functions becuase C++ is a cross-platform language. These are best described as 3rd party functions. The functions you yourself write are known as user-defined functions.
A header file is used in some languages to declare functions that will be used but are not yet defined in the current source code. This is primarily used by C and C++, and usually for library functions and user-defined functions that are stored in separate files and folders than the main source code file.
Rephrase your question so it is comprehensible.