有符号与无符号 整形变量 相加和比较

int main() {
	unsigned int a = 1;
	int b = -20;
	std::cout << ((a + b > 6) ? ">6" : "<6");
	return 0;
}

输出  >6
因为：int 转为unsigned int

int main() {
	unsigned int a = 1;
	int b = -1;
	std::cout << ((a + b > 1) ? ">1" : "<1");
	return 0;
}

输出  <1
因为： - 1   32位全为1，再加上1。结果为0

	int main() {
	unsigned int a = 1;
	char  b = -20;
	unsigned int c = (unsigned int)b;//c=4294967276
	unsigned char d = (unsigned char)b;//d=236
	std::cout << (((c = a + b) > 1) ? ">1" : "<1");//c=4294967277

	return 0;
}

输出  >1
因为：由注释得：将char型 - 20  转成了 unsigned int 进行运算