In C++, there are three distinct character types:

1. char
2. signed char
3. unsigned char

1. char

If you are using character types for text, use the unqualified char:

• it is the type of character literals like 'a' or '0' (in C++ only, in C their type is int)
• it is the type that makes up C strings like "abcde"

It also works out as a number value, but it is unspecified whether that value is treated as signed or unsigned. Beware character comparisons through inequalities - although if you limit yourself to ASCII (0-127) you're just about safe.

2. signed char/ 3. unsigned char

If you are using character types as numbers, use:

• signed char, which gives you at least the -127 to 127 range. (-128 to 127 is common)
• unsigned char, which gives you at least the 0 to 255 range. This might be useful for displaying an octet e.g. as hex value.

"At least", because the C++ standard only gives the minimum range of values that each numeric type is required to cover. sizeof (char) is required to be 1 (i.e. one byte), but a byte could in theory be for example 32 bits. sizeof would still be report its size as 1 - meaning that you could have sizeof (char) == sizeof (long) == 1.

There's no dedicated "character type" in C language. char is an integer type, same (in that regard) as int, short and other integer types. char just happens to be the smallest integer type. So, just like any other integer type, it can be signed or unsigned.

It is true that (as the name suggests) char is mostly intended to be used to represent characters. But characters in C are represented by their integer "codes", so there's nothing unusual in the fact that an integer type char is used to serve that purpose.

The only general difference between char and other integer types is that plain char is not synonymous with signed char, while with other integer types the signed modifier is optional/implied.

Where is unsigned char used in C ( please tell about some real-world examples )? Why would we need both char and unsigned char?

signed or unsigned are properties of the different C data types (char, short, int, etc...). So it's not a question of whether we need both, both come automatically as part of how C is defined.

Char ranges from -127 to 128 ( 8-bit integer ) Unsigned Char ranges from 0 to 255 ( 8-bit integer )

While that's true for most of the platforms out there, there's nothing garanting that char will be signed. In fact on ARM platforms, it's unsigned. See this fix: http://www.spinics.net/lists/linux-btrfs/msg20653.html as an example of real-world bug introduced by assuming that char is signed.

If the purpose is to store ASCII, why would we need both?

The thing is, the purpose is not to store ASCII. It happens to be used to store ASCII but it's a not a necessity.

char a = 127;

unsigned char b = 255;

When I print it using std::cout. It gives me different characters. Can you explain why? ( I'm using Microsoft vs11 compiler

I think what you're looking for is the following:

#include <iostream>

int main(void)
{
        char a = -1; 
        unsigned char b = 255;
        std::cout << a << std::endl << b << std::endl;
        return 0;
}

That is '-1' signed will be equal to '255' unsigned. Please note that this is heavily implementation dependent, and there's nothing that guarantees it will work accross all platforms and compilers.

Declare your ch as

unsigned char ch = 212 ;

And your printf will work.