What is an unsigned char?

Question

In C/C++, what an `unsigned char` is used for? How is it different from a regular `char`?

Answer 1

The main differnce comes in range and memory allocation of characters while executing the program. A signed char is same as an ordinary char and has a range from -128 to +127; whereas, an unsigned char has a range from 0 to 255.

Answer 2

Short answer:

In C/C++, the SAME bits are used in both unsigned and signed chars, but they are INTERPRETED differently by the compiler.

An unsigned char can be used for a number from 0 to 255,

and a signed char for a number from -128 to 127.

(Note: on the Internet, there are conflicting answers for signed char, but it *must* be this range, see example below...)

Here is an example with a four-bit char for educational purposes to save space...

Say a char had 4 bits (it doesn't, but say it does), then

bits unsigned signed

char char

0000 0 0

0001 1 1

0010 2 2

0011 3 3

0100 4 4

0101 5 5

0110 6 6

0111 7 7

1000 8 -8 same bits are interpreted differently

1001 9 -7

1010 10 -6

1011 11 -5

1100 12 -4

1101 13 -3

1110 14 -2

1111 15 -1 biggest unsigned is smallest negative signed

How does this work? Because 1 + -1 = 0, right?

In bits, 1111 + 0001 = 10000 (but there are only 4 bits, so the highest one is thrown away, then we have

1111 + 0001 = (1)0000 we ignore the highest 1

similarly

1110 + 0010 = (1)0000, -2 + 2 == (1)0000 (both numbers are signed)

1101 + 0011 = (1)0000, -3 + 3 == (1)0000

1100 + 0100 = (1)0000, -4 + 4 == (1)0000

and so on

What if both numbers are unsigned?

then

1111 + 0001 == (1)0000, 15 + 1 == (1)0000 (remember, in 4-bit chars, 15 is the largest number)

1110 + 0010 == (1)0000, 14 + 2 == (1)0000

1101 + 0011 == (1)0000, 13 + 3 == (1)0000

1100 + 0100 == (1)0000, 12 + 4 == (1)0000

Wait, what?! How can 1111 == 15 (for an unsigned char), AND 1111 == -1 (for a signed char)?

It's all a matter of interpretation.

The SAME bits are present in both cases, but if you tell the compiler

those bits represent an unsigned char, it will interpret them in one way,

and if you tell them they represent a signed char, the computer will interpret them another way.

Hope that helps.