Program:

    #include<iostream.h>
    #include<conio.h>

    class sumofdigit
    {
    private:
    int sum,n;
    public:
    inline sumofdigit()
    {
    sum=0;
    cout<<"\n\nUsing default constructor";
    cout<<"\n\nSum is:"<<sum;
    }
    sumofdigit(int n);
    sumofdigit1()
    {
    cout<<"\n\nDestructor --> memory clearence";
    }
    };
    sumofdigit::sumofdigit(int n)
    {
    sum=0;
    if(n>=10)
    while(n>=10)
    {
    sum=sum+(n%10);
    n=n/10;
    }
    sum=sum+n;
    cout<<"\n\nSum of digit is: "<<sum;
    if(sum>10)
    {
    n=sum;
    sum=0;
    while(n>=10)
    {
    sum=sum+(n%10);
    n=n/10;
    }
    sum=sum+n;
    }
    cout<<"\n\nSum of digit is: "<<sum;
    sumofdigit1();
    }
    void main()
    {
    int n;
    clrscr();
    cout<<"\n\tSUM OF DIGIT USING CONSTRUCTOR";
    cout<<"\n\nEnter the number:";
    cin>>n;
    sumofdigit s;
    sumofdigit s1(n);
    getch();
    }