I can use some enlightment!

[kikirikou]

Hello everyone,i am reading Strustrups book and i found a spot in a example of his code which i don't fully understant.In this example we have a class Date which saves three variables,date,month,year.We have also a constructor which gives values to these variables by default.I will so you what i mean.

This is the code

#include<iostream>
using namespace std;

class Date
{
        int d,m,y;
    public:
        Date(int dd=0,int mm=0,int yy=0);
        void show();

}today;

Date::Date(int dd,int mm,int yy)
{
    d=dd?dd:today.d;
    m=mm?mm:today.m;
    y=yy?yy:today.y;
}

void Date::show()
{
    cout<<"date:"<<d<<",month :"<<m<<",year:"<<y<<endl;
}


int main()
{
    Date today1;
    Date today2(10,10,1980);

    today1.show();
    today2.show();

    return 0;
}

Well in this point the class cheks if the specific date which i want to pass i acceptable.

Date::Date(int dd,int mm,int yy)
{
   [code] d=dd?dd:today.d;
    m=mm?mm:today.m;
    y=yy?yy:today.y;
}

Actually i don't understant this

 d=dd?dd:today.d;
    m=mm?mm:today.m;
    y=yy?yy:today.y;

It means for example compare the zero value with the given value and if they are not equal return the new value?I am a litle bit confused.Can anyone help me? Thanks anyway.

[kfmfe04]

It says if dd is non-zero, assign the value to d,
otherwise, assign the value of today.d to d.

So the net-effect of that constructor is this:
1. If you enter non-zero values for dd, mm, yy, assign these values to my guts.
2. Otherwise (dd, mm, yy are zero), default my guts to today's ymd.

[kikirikou]

ok so simple ,thanks !