C++重载运算符、构造函数等

我创建了自己的四种方法来将字符串处理为数字:

std::string addStrings(std::string,std::string);
std::string subtractStrings(std::string,std::string);
std::string multiplyStrings(std::string,std::string);
std::string divideStrings(std::string,std::string);

然后我决定创建大数的类(称为bin)。我对复制构造函数和复制赋值运算符有点陌生,所以我需要你的帮助来修复我的代码:

class bin{
    private:
        std::string value;
    public:
        bin(){}
        bin(const char* v1){
            value = v1;
        }
        bin(std::string v1){
            value = v1;
        }
        bin(const bin& other){
            value = other.value;
        }
        bin& operator=(const bin& other){
            value = other.value;
            return *this;
        }
        bin& operator=(const char* v1){
            value = v1;
            return *this;
        }
        std::string getValue() const{
            return value;
        }
        friend std::ostream& operator<<(std::ostream&,bin&);
};

std::ostream& operator<<(std::ostream& out,bin& v){
    out << v.value;
    return out;
}
bin operator+(bin& value1,bin& value2){
    return bin(addStrings(value1.getValue(),value2.getValue()));
}
bin operator-(bin& value1,bin& value2){
    return bin(subtractStrings(value1.getValue(),value2.getValue()));
}
bin operator*(bin& value1,bin& value2){
    return bin(multiplyStrings(value1.getValue(),value2.getValue()));
}
bin operator/(bin& value1,bin& value2){
    return bin(divideStrings(value1.getValue(),value2.getValue()));
}

为什么这样做有效:

bin d = a/c;
std::cout << d << std::endl;

但这并不是:

标准::cout<&书信电报;a/c;

(a和c较早宣布)。此外,运算符链接也不起作用,例如:

bin d = a * b + d;

投掷:

no match for operator* (operands are bin and bin).

非常感谢。