According to the C++23 standard, what is the output of this program?
#include <iostream>
int main() {
int i = '3' - '2';
std::cout << i;
}The value of each decimal character in the character set is one greater than the value of the previous.
1
'3' and '2' are both ordinary character literals, with type char. But we don't know which values they have! That's up to the implementation:
A character-literal with a c-char-sequence consisting of a single basic-c-char, simple-escape-sequence, or universal-character-name is the code unit value of the specified character as encoded in the literal's associated character encoding.
operator- subtracts the value of the second operand from the value of the first operand. But how can we know what the result is, when we don't know the values of the operands?
The code unit value of each decimal digit character after the digit
0(U+0030) shall be one greater than the value of the previous.
So we know that the difference between '3' and '2' is 1, even if we don't know their actual values. Importantly, this is only true for decimal digits, and not for instance for regular letters. There is no guarantee that 'b' - 'a' is 1.