NULL, NUL, '\ 0', 0, and EOF

0Is an integer constant,

'\ 0'Is a character constant,

NulIs the name of the character constant.

NULLIs a macro defined in several standard headers,

All of these are ** not * interchangeable:

NULL is to be used for pointers only since it may be defined(Void *) 0), This wocould cause problems with anything but pointers.

0 can be used anywhere, it is the generic symbol for each type's zero value and the compiler will sort things out.

'\ 0' shoshould be used only in a character context.

Nul is not defined in C or C ++, it shouldn't be used unless you define it yourself in a suitable manner, like:

# Define nul '\ 0'

EOF: It is usually defined as-1, and the end mark of the file, usually ctrl + z.

For more information about EOF, see http://www.ruanyifeng.com/blog/2011/11/eof.html.