cin

c++学习cin的使用总结
cin属于istream类的对象（还没搞懂什么是类，c++萌新，大佬轻喷）
先说一下我为什么会写这篇博客：
下午照着c++primerplus做题的时候遇到一个难点，到网上找到答案之后发现
cin还有这么多用法`：

basic_istream& __CLR_OR_THIS_CALL operator>>(int& _Val) { // extract an int
    static_assert(sizeof(int) == sizeof(long), "Bad overflow assumptions due to sizeof(int) != sizeof(long)");
    long _Result = _Val;
    _Common_extract_with_num_get(_Result);
    _Val = _Result;
    return *this;
}

basic_istream& __CLR_OR_THIS_CALL operator>>(unsigned int& _Val) { // extract an unsigned int
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(long& _Val) { // extract a long
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(unsigned long& _Val) { // extract an unsigned long
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(long long& _Val) { // extract a long long
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(unsigned long long& _Val) { // extract an unsigned long long
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(float& _Val) { // extract a float
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(double& _Val) { // extract a double
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(long double& _Val) { // extract a long double
    return _Common_extract_with_num_get(_Val);
}

basic_istream& __CLR_OR_THIS_CALL operator>>(void*& _Val) { // extract a void pointer
    return _Common_extract_with_num_get(_Val);
}`

这些是我在头文件istreaml里面找到的，发现"<<"操作符和函数很类似，当输入符合参数类型的数据时，函数返回一个非零数，否则返回“0”。