what is the unsigned datatype?

Solution 1:

unsigned really is a shorthand for unsigned int, and so defined in standard C.

Solution 2:

unsigned means unsigned int. signed means signed int. Using just unsigned is a lazy way of declaring an unsigned int in C. Yes this is ANSI.

Solution 3:

Historically in C, if you omitted a datatype "int" was assumed. So "unsigned" is a shorthand for "unsigned int". This has been considered bad practice for a long time, but there is still a fair amount of code out there that uses it.

Solution 4:

in C, unsigned is a shortcut for unsigned int.

You have the same for long that is a shortcut for long int

And it is also possible to declare a unsigned long (it will be a unsigned long int).

This is in the ANSI standard

Solution 5:

In C and C++

unsigned = unsigned int (Integer type)
signed   = signed int (Integer type)

An unsigned integer containing n bits can have a value between 0 and (2^n-1) , which is 2^n different values.

An unsigned integer is either positive or zero.

Signed integers are stored in a computer using 2's complement.