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My little program:
#include <stdio.h>
int main() {
signed char c = -128;
c = -c;
printf("%d", c);
return 0;
}
print:
-128
Is minus (-) operator portable across CPU?
632
You would use a signed char when you need to represent a quantity in the range [-128, 127] and you can't (for whatever reason) spare more than a single byte to do it.
unsigned char is a character datatype where the variable consumes all the 8 bits of the memory and there is no sign bit (which is there in signed char). So it means that the range of unsigned char data type ranges from 0 to 255.
For example, if we want to store char 'A' in computer, the corresponding ASCII value will be stored in computer. ASCII value for capital A is 65. To store character value, computer will allocate 1 byte (8 bit) memory. 65 will converted into binary form which is (1000001) 2.
The operand of the unary minus first undergoes standard promitions, so it is of type int, which can represent the value -128. The result of the operation is the value 128, also of type int. The conversion from int to signed char, being a narrowing of signed types, is implementation-defined.
(Your implementation seems to do a simple wrap-around: 125, 126, 127, -128, -127, ...)
107
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