C++Primer第五版：练习2.3 2.4

练习2.3

#include<iostream>

int main()
{
    
    
	unsigned u = 10, u2 = 42;
	std::cout << u2 - u << std::endl;
	std::cout << u - u2 << std::endl;

	int i = 10, i2 = 42;
	std::cout << i2 - i << std::endl;
	std::cout << i - i2 << std::endl;
	std::cout << i - u << std::endl;
	std::cout << u - i << std::endl;
}

练习2.4（略）