Where does negative ASCII value used?

Answer 1

There is no such thing as a negative ASCII value. ASCII values are always in the range 0-255. In C++, a char is defined as an unsigned integer of 8-bits in length (wide chars are unsigned integers of 16-bit length). Since they are unsigned, they can never be negative.

C differs from C++ in that a C char is generally represented as a signed integer (typically 32-bits on a 32-bit system). However, when cast as a character, only the low-order byte is used, which effectively ignores the sign in the high-order byte. In other words, the absolute value is used, regardless of the sign. The same applies to wide characters.