Signed and unsigned integers?

Question

Could someone please explain the two to me because I have to give an explanation of them both in my assignment.

I know what a normal integer is of course and have used the following to describe it:

"An integer is a whole number which can be positive, negative and zero but it cannot have decimal points."

But I'm just not sure about signed and unsigned.

Thanks

Answer 1

In most languages when you declare an integer, you are declaring a signed integer. If you want to declare an unsigned integer you have to specifically tell the compiler. e.g. in c#

int a; // Signed int
uint b; // Unsigned int.

The difference is that in a signed int, one of the bits is used to indicate if the number is positive or negative. In and unsigned int, that bit is used to hold a value. The effect is that you can hold twice the absolute values in an unsigned in as you can in a signed int. Or more plainly, the range of the C# integer is -2,147,483,648 to 2,147,483,647 while the range of the uint is 0 to 4,294,967,295. Both data types are 32 bit datatypes.

Answer 2

The difference between a signed and unsigned integer is that one byte of the integer is required to hold the sign.

For instance, with two binary digits you can have the following:

Base 2   Base 10
00       0
01       1
10       2
11       3

However, if we take the first digit to mean negative (0) or positive (1)

Base 2   Base 10
01       -1
00       0
10       1
11       2

Or, if we wanted 1 to be negatiave, and 0 to be positive:

Base 2   Base 10
01       1
00       0
10       -1
11       -2

For further reading, check out the Wikepedia article on Two's compliment