Как увеличить дату на 10 дней?

# include <iostream>
# include <iomanip>
# include <cmath>
# include <ctime>
using namespace std;
void main()
{
    int a = 0, b = 0, c = 0, d = 0, e = 0, f = 0, g = 0, h = 0, i = 0, j = 0, k = 0, l = 0, m = 0, n = 0, o = 0, p = 0, q = 0, r = 0;
    cout<<"\n\t\tPATIENT CARD \n\n -------------------------------------------------"<<endl;
    cout<<"\t Number of the card:"<<endl;
    cin>>a;
    cout<<"\t Date  of arrival to the hospital:"<<endl;
    cin>>b;
    cout<<"\t Date  of leaving the hospital:"<<b+10<<endl;
    cin>>c;
    cout<<"\t Department, chamber:"<<endl;
    cin>>d;
    cout<<"\t First name:"<<endl;
    cin>>e;
    cout<<"\t Last name:"<<endl;
    cin>>f;
    cout<<"\t Domicile:"<<endl;
    cin>>g;
    cout<<"\t Job:"<<endl;
    cin>>h;
    cout<<"\t Who sent the patient:"<<endl;
    cin>>i;
    cout<<"\t Diagnosis at admission:"<<endl;
    cin>>j;
    cout<<"\t patient's complaints and anamnesis:"<<endl;
    cin>>k;
    cout<<"\t Results of examination:"<<endl;
    cin>>l;
    cout<<"\t Final diagnosis"<<endl;
    cin>>m;
    cout<<"\t Treatment"<<endl;
    cin>>n;
    cout<<"\t Results of treatment"<<endl;
    cin>>o;
    cout<<"\t Length of hospital stay"<<endl;
    cin>>p;
    cout<<"\t Treating physician"<<endl;
    cin>>q;
    cout<<"\t Head of department"<<endl;
    cin>>r;
}