对时间的时分秒分别加上n

#include <iostream>

using namespace std;
class Time
{
public:
    Time (int a,int b,int c);
    void set_time();
    void show_time();
    void add_a_sec(int);
    void add_a_minute(int);
    void add_an_hour(int);
private:
    bool is_time(int,int,int);
    int hour;
    int minute;
    int sec;
};
Time::Time(int a,int b,int c)
{
    hour=a;
    minute=b;
    sec=c;
}
void  Time::set_time()
{
    char c1,c2;
    cout<<"请输入时间(格式hh:mm:ss)"<<endl;
    while(1)
    {
        cin>>hour>>c1>>minute>>c2>>sec;
        if(c1!=':' || c2!=':')
            cout<<"格式不正确重输"<<endl;
        else if(!is_time(hour,minute,sec))
            cout<<"时间非法，请重新输入"<<endl;
        else
        
            
            break;
        
    }
}
void  Time::show_time()
{
   
    cout<<hour<<":"<<minute<<":"<<sec<<endl;
}
bool Time::is_time(int h,int m,int s)
{
    if(h<0 || h>60 || m<0 || m>60 || s<0 || s>60)
        return false;
    else
        return true;
}
void Time::add_a_sec(int n)
{
    
    if((sec+n)>=60)
    {
        sec=(sec+n)%60;
        add_a_minute(n/60);
        
    }
    else
        sec+=n;
    
}
void  Time::add_a_minute(int n)
{
    
    if((minute+n)>=60)
    {
        minute=(minute+n)%60;
        add_an_hour(n/60);
    }
    else
        minute+=n;
   
}
void Time::add_an_hour(int n)
{
    
    if((hour+n)>=24)
    {
        hour=(hour+n)%24;
        add_an_hour(n/24);
        
    }
    else
        hour+=n;
   
}


int main()
{
    Time t1(0,0,0);
    int n;
    cout<<"请输入要增加的时间n"<<endl;
    cin>>n;
    
    t1.set_time();
    //t1.show_time();
    t1.add_a_sec(n);
    t1.add_a_minute(n);
    t1.add_an_hour(n);
    t1.show_time();
    return 0;
}