No predefined 'header' function in the standard C libraries. There are header files, if that's what you mean.
Platform dependent, possibly LIBC.LIB or something like that.
list of header files in c and function prototype associated with each file
Include the header file math.h and use the function acos(d)
int86 is a function in TurboC, header dos.h, consult the built-in help.
Constants, typedefs, function prototypes. If you want to know more, load it into a text editor.
to include the header files.
There are no 'sections' in C source, you can define functions anywhere, except inside another function or variable/type definition.
You need to #include the header file that contains the missing function's declaration.
it is sqrt in header math.h
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.
It's 1405 in my Linux box.
All function interfaces must be declared before they can be used. This is known as a forward declaration and is strictly enforced in C++ (but not in C). To facilitate this, interfaces are typically placed in a header file which can then be included in every source file that requires access to that function. The interface need not be defined (implemented) in the header unless the function is a template function. Typically, implementations are kept separate from interfaces (template function implementations are kept in the header but typically separated from the interface) since the interface contains everything the user needs to know in order to make use of the function.