How to competently implement decomposition?

Question

C++ / C#

I started to study OOP in C ++, I faced the following task:
Purpose of the work: Obtaining the skills of modular decomposition of the subject area, creating modules. Interface development.
Task: Develop a program consisting of three modules in accordance with the specified version of the task. The first module is the main program code; the second contains interfaces; the third module is the implementation of these interfaces. The number of data structures ("objects") is at least five.
EXAMPLE
Let it be required to develop the program "Clock". The time is stored in the TTime structure (hours, minutes, seconds), which in turn is part of the Date structure. Methods allow you to change the current time and display the time on the screen.

typedef struct ttime {
  int hours; int minute; int sec;
};

struct date {
  ttime time;
  void settime(int, int, int);
  void printtime();
};

#include <stdio.h>
#include "date.h"

void date::settime(int h, int m, int s)
{
  time.hours = h;
  time.minute = m;
  time.sec= s;
}

void date::printtime()
{
  printf("%i:%i:%i", time.hours, time.minute, time.sec);
}

#include <stdio.h>
#include "date.h"

int main()
{
  date a;
  a.settime(23,43,10);
  a.printtime();
  getchar();
  return 0;
}

I need to do the same for the challenge:
Martial Arts Tournament.
(Sorry for the layout, posting from mobile)

Answer 1

typedef struct ttime {
C, ++ doesn't need a typedef.
And finally use code tags.
Strange naming, they usually write hour.

struct date {
ttime time;

So where is the measurement?
My architecture.
1. Time. Getting time from the system, comparison, output to the console.
2. Clock. Keep the last time. The “tick” command is to get the time, compare it with the last one, in case of inequality, save the new one and output it to the console.
3. External cycle (can be both in hours and outside). The clock ticks, pauses a little, and checks for a keystroke.
There will be no five objects, and Date is only needed if you really work with the date. I would, in order to bring the number of objects to the desired one, would make a date (date), time (time) and date-time (stamp).
For a martial arts tournament (for simplicity - without weight categories).
• Fighter: name, all information about him like city, club and titles.
• Stub: pointer to Fight + enum (Winner/Loser) - where the participant comes from. There is no pointer to Fight - then TBD (that is, not determined).
• Participant: pointer to Fighter + struct stub.
• Fight: number, two Participants, date/time, who won (0/1), reason for victory (not yet fought, KO, TKO, by points, no-show…)
• Tournament: contains a list of fights and a table of results.
You can also break the dependency loop by tweaking the FightInfo interface, making the Stub FightInfo* instead of Fight*, and having Fight implement FightInfo.