Calculate Pace (Running Program)

// pace-2.cpp  --  To calculate pace of a run
// author : Steven Taylor
// 21 Dec, 2007.

#include <iostream>
using namespace std;
const int SECS_IN_MIN = 60;
const int MINS_IN_HOUR = 60;
const int SECS_IN_HOUR = 3600;

struct hms
{
    int hour;
    int min;
    int sec;
};
const hms & pace_is(double distance, hms  & duration, hms & rate);

int main()
{
    double distance;
    hms duration;
    hms perkm = {0,0,0};
   
    cout << "Enter distance (km's) run: ";
    while (!(cin >> distance))
    {
        cout << "\nMust enter a number - re-enter: ";
        cin.clear();
        while (cin.get() != '\n')
            continue;
    }
    cout << "\nEnter duration of run - firstly - hours: ";
    while (!(cin >> duration.hour))
    {
       cout << "\nMust be an integer number - re-enter - hours: ";
       cin.clear();
       while (cin.get() != '\n')
           ;
    }
    cout << "\nEnter minutes (0-59): ";
    while (!(cin >> duration.min) || duration.min >= MINS_IN_HOUR)
    {
        cout << "\nMinutes must be 0 - 59, re-enter - minutes: ";
        cin.clear();
        while (cin.get() != '\n')
            ;
    }
    cout << "\nEnter seconds (0 - 59): ";
    while (!(cin >> duration.sec) || duration.sec >= SECS_IN_MIN)
    {
        cout << "\nSeconds must be 0 - 59, re-enter - seconds: ";
        cin.clear();
        while (cin.get() != '\n')
            ;
    }

    perkm = pace_is(distance,duration,perkm);
   
    cout << "\nThe pace per km is : ";
    if (perkm.hour > 0)
        cout << perkm.hour << ":";
    cout << perkm.min << ":" << perkm.sec << endl;
   
    // exit routine
    cout << "\n\n...Press ENTER to Exit System...";
    cin.clear();
    while (cin.get() != '\n')
        continue;
    cin.get();
    return 0;
}

const hms & pace_is(double distance, hms & d, hms & rate)
{
       
    int total_secs = (d.hour * SECS_IN_HOUR) + (d.min * SECS_IN_MIN) + d.sec;
    double secs_per_km = total_secs / distance;
       
 
    if (secs_per_km > SECS_IN_HOUR)
    {
        rate.hour = secs_per_km / SECS_IN_HOUR;
        secs_per_km = (int)secs_per_km % SECS_IN_HOUR;
    }
    if (secs_per_km > 0)
    {
        rate.min = secs_per_km / MINS_IN_HOUR;
        rate.sec = (int)secs_per_km % MINS_IN_HOUR;
    }
        return rate;
}