c++ 类的数据成员初始化

class First{
public:
    int num = 0;//错误
    const int num1 = 0;//错误
    static int num2 = 0;//错误
    static const int num3 = 0;//正确，只有静态常量整型数据成员才可以在类中初始化
    string str = "0";//错误
    const string str1 = "0";//错误
    static string str2 = "0";//错误
    static const string str3 = "0";//错误
    float fnum = 0;//错误
    const float fnum1 = 0;//错误
    static float fnum2 = 0;//错误
    static const float fnum3 = 0;//错误
};