Algoritmos: Repartir el tiempo total de una tarea a lo largo de varios días en C

/**
*************************************************************
* @file calcula_horas.c
*************************************************************/

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <string.h>

typedef struct
{
  int hours;
  int minutes;
  float raw;
} Thm;

time_t getTime(int day, int month, int year);
int calculateDaysInRange(int daysInRange[7], time_t start, time_t end);
int calculateTotalDays(int workDays[7], int daysInRange[7]);
int calculateHoursADay(Thm *result, int totalDays, int hoursToWork, int totalHours);

int main(int argc, char *argv[])
{
  int error;
  int i ;
  int totalDays;
  time_t start = getTime(1, 6, 2013);
  time_t end = getTime(18, 6, 2013);
  /* Which days can we work in this task? */
  /* Starts on sunday */
  /* YOU MUST FILL THIS ARRAY */
  int workDays[7] = { 0, 1, 0, 1, 1, 0, 1};
  int hoursToWork=4;
  /* Number of sundays, mondays, tuesdays, wednesdays, etc between start and end date */
  int daysInRange[7] = { 0, 0, 0, 0, 0, 0, 0};
  Thm thm;

  error = calculateDaysInRange(daysInRange, start, end);
  if (!error)
    {
      totalDays = calculateTotalDays(workDays, daysInRange);
      error = calculateHoursADay(&thm, totalDays, hoursToWork, 42);
      if (!error)
    {
      printf ("From: %s\n", ctime(&start));
      printf ("To: %s\n", ctime(&end));
      for (i=0; i<7; i++)
        printf ("Day %d: %d\n", i, daysInRange[i]);
      printf ("total days: %d\n", totalDays);
      printf ("Hours a Day: %d hours and %d minutes (%f h)\n", thm.hours, thm.minutes, thm.raw);
    }
      else
    {
      printf("You can't spend more time than available\n");
      printf("But you should work %d hours and %d minutes a day to complete your task.\n", thm.hours, thm.minutes);
    }
    }
  else
    printf ("There was a problem...\n");
  return EXIT_SUCCESS;
}

time_t getTime(int day, int month, int year)
{
  struct tm tm;

  /* Clean tm struct */
  memset(&tm, 0x00, sizeof(tm));
  tm.tm_mday = day;
  tm.tm_mon = month-1;
  tm.tm_year = year-1900;

  return mktime(&tm);
}

int calculateDaysInRange(int daysInRange[7], time_t start, time_t end)
{
  time_t diff = difftime(end, start);
  struct tm *start_tm = localtime(&start);

  int totalDays = 1 + diff / 86400; /* From day 1 to 10, there are 10 days (10 - 1 + 1) */
  /* So, all days in the week will be (totalDays/7) times in the date range except
     (totalDays%7) days from the starting date, they will be (totalDays/7)+1 times */
  int repeat = totalDays / 7;
  int i;
  for (i=0; i<7; ++i)
    daysInRange[i]=repeat;

  for (i=0; i<totalDays%7; ++i)
    daysInRange[(start_tm->tm_wday+i)%7]++;

  return 0;         /* No error */
}

int calculateTotalDays(int workDays[7], int daysInRange[7])
{
  int i;
  int total=0;

  for (i=0; i<7; ++i)
    {
      daysInRange[i]=(workDays[i])?daysInRange[i]:0;
      total+=daysInRange[i];
    }
  return total;
}

int calculateHoursADay(Thm *result, int totalDays, int hoursToWork, int totalHours)
{
  int availableHours = totalDays*hoursToWork;

  result->hours= totalHours/totalDays;
  result->minutes = (totalHours%totalDays)*60/totalDays;
  result->raw=(float)totalHours/totalDays;

  if (availableHours<totalHours)
    return -1;

  return 0;
}