无符号类型赋值负数，以及求绝对值

#include <iostream>
#include <cmath>

int main()
{
    unsigned char i = 0 ;

    i = -1 ;
    std::cout<<"i="<<(int)i<<std::endl;

    i = -2 ;
    std::cout<<"i="<<(int)i<<std::endl;

    i = -3 ;
    std::cout<<"i="<<(int)i<<std::endl;

    i = 256 ;
    std::cout<<"i="<<(int)i<<std::endl;

    i = 257 ;
    std::cout<<"i="<<(int)i<<std::endl;

    i = 258 ;
    std::cout<<"i="<<(int)i<<std::endl;

    std::cout<<"---------------------------"<<std::endl;

    std::cout<<(int)std::abs(-100)<<std::endl;

    std::cout<<std::abs(-100.0)<<std::endl;

    std::cout<<std::abs(-100.0D)<<std::endl;

    return 0;
}