Opgaveløsning:
Iterativ løsning af 'uger, dage, timer, minutter og sekunder' opgaven

#include <stdio.h>
#define SECONDS_PER_MINUTE 60
#define SECONDS_PER_HOUR (SECONDS_PER_MINUTE * 60)
#define SECONDS_PER_DAY (SECONDS_PER_HOUR* 24)
#define SECONDS_PER_WEEK (SECONDS_PER_DAY * 7)
#define UNIT_COUNT 5

void decompose_seconds_to_units(int input_seconds, int result_units[]);

int second_amount[] = {SECONDS_PER_WEEK, SECONDS_PER_DAY, SECONDS_PER_HOUR, SECONDS_PER_MINUTE};
char *units[] = {"weeks", "days", "hours", "minutes", "seconds"}; 

int main(void){
  int input_seconds, i;
  int result_units[UNIT_COUNT];

  /* Prompt for input: */
  printf("Read a non-negative number of seconds: ");
  scanf("%d", &input_seconds);

  decompose_seconds_to_units(input_seconds, result_units);

  /* Print the calculated units */
  for(i = 0; i < UNIT_COUNT; ++i)
    printf("%d %s   ", result_units[i], units[i]);

  return 0;
}

/* Decompose the seconds in input_seconds to the units enumerated in the global array units */
void decompose_seconds_to_units(int input_seconds, int result_units[]){
  int i = 0,
      rest_seconds = input_seconds,
      parts = sizeof(second_amount) / sizeof(int);

  while (i < parts){
    result_units[i] = rest_seconds / second_amount[i];
    rest_seconds = rest_seconds % second_amount[i];
    ++i;
  }
  result_units[i] = rest_seconds;
}