Прибавление к времени заданного количества секунд

void time_to_seconds(size_t &time, size_t &hrs, size_t &min, size_t &sec); 
void seconds_to_time(size_t &time, size_t &hrs, size_t &min, size_t &sec); 
 
 
int main(){
    size_t hrs = 11;
    size_t min = 15;
    size_t sec = 23;
    size_t time= 0;
    time_to_seconds(time, hrs, min, sec);
    time += 120;
    seconds_to_time(time, hrs, min, sec);
    cout<<hrs<<" : "<<min<<" : "<<sec<<endl;
    return 0;
}
 
void time_to_seconds(size_t &time, size_t &hrs, size_t &min, size_t &sec){
    time = sec + min*60 + hrs*3600;
}
 
void seconds_to_time(size_t &time, size_t &hrs, size_t &min, size_t &sec){
    hrs = time / 3600;
    time= time % 3600;
    min = time / 60;
    time= time % 60;
    sec = time;
}

#include <iostream>
#include <iomanip>
 
int main()
{
    int hours, minutes, seconds,
        seconds_passed;
    char delimeter;
 
    std::cin >> hours >> delimeter >> minutes >> delimeter >> seconds
        >> seconds_passed;
 
    const int seconds_in_minute = 60,
        mintues_in_hour = 60,
        hours_in_day = 24;
 
    seconds += seconds_passed;
    minutes += seconds / seconds_in_minute;
    seconds %= seconds_in_minute;
 
    hours += minutes / mintues_in_hour;
    minutes %=mintues_in_hour;
 
    hours %= hours_in_day;
 
    std::cout << std::setfill('0');
    std::cout << std::setw(2) << hours << ':'
        << std::setw(2) << minutes << ':'
        << std::setw(2) << seconds;
}