rk1

#include <assert.h>
#include <alloca.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <getopt.h>

#define BUFFER_LENGTH 250

typedef struct _data_t
{
  int hours_wasted, coffee_drunk_ml, fastfood_eaten;
  float completion_coeff;
  char comment[BUFFER_LENGTH];
}  data_t;

typedef union _mudata_t
{
  int i;
  float f;
  char s[BUFFER_LENGTH];
} mudata_t;

void print_data(const data_t* data)
{
  printf(
    "{\n %s: total wasted %d hours to complete %.3f percent of that crap\n consumed %d ml of coffee and %d kg of nasty food \n}\n",
    data->comment,
    data->hours_wasted,
    data->completion_coeff,
    data->coffee_drunk_ml,
    data->fastfood_eaten
  );
}

void ha_modify_data(data_t* data, const char* format, const mudata_t* mudata)
{
  size_t i, j, n;

  j = 0;
  n = strlen(format);

  for(i = 0; i < n; i++)
  {
    switch(format[i])
    {
      case 'h':
        data->hours_wasted = mudata[j++].i;
        break;
      case 'c':
        data->completion_coeff = mudata[j++].f;
        break;
      case 'm':
        strcpy(data->comment, mudata[j++].s);
        break;
      case 'd':
        data->coffee_drunk_ml = mudata[j++].i;
        break;
      case 'f':
        data->fastfood_eaten = mudata[j++].i;
        break;
      default:
        break;
    }
  }

}

void va_modify_data(data_t* data, const char* format, ...)
{
  va_list args;
  size_t i, n;

  n = strlen(format);

  va_start(args, format);

  for(i = 0; i < n; i++)
  {
    switch(format[i])
    {
      case 'h':
        data->hours_wasted = va_arg(args, int);
        break;
      case 'c':
        data->completion_coeff = (float)va_arg(args, double);
        break;
      case 'm':
        strcpy(data->comment, va_arg(args, const char*));
        break;
      case 'd':
        data->coffee_drunk_ml = va_arg(args, int);
        break;
      case 'f':
        data->fastfood_eaten = va_arg(args, int);
        break;
      default:
        break;
    }
  }

  va_end(args);
}

int main(int argc, char** argv)
{
  int opt;
  data_t course_proj;
  mudata_t* mvalues = NULL;

  printf(":: initial values ::\n");
  course_proj.hours_wasted = 1;
  course_proj.completion_coeff = 0.001f;
  course_proj.coffee_drunk_ml = 300;
  course_proj.fastfood_eaten = 0;
  strcpy(course_proj.comment, "gaming is evil");
  print_data(&course_proj);

  printf(":: heterogenous argument array modification ::\n");
  mvalues = alloca(2 * sizeof(mudata_t));
  assert(mvalues);
  mvalues[0].i = 4;
  mvalues[1].f = 0.002f;
  ha_modify_data(&course_proj, "hc", mvalues);
  print_data(&course_proj);

  printf(":: variadic function modification ::\n");
  va_modify_data(&course_proj, "dmf", 2100, "I hate electrotechnics", 1);
  print_data(&course_proj);

  printf(":: command line argument modification ::\n");
  while((opt = getopt(argc, argv, "h:c:m:d:f:")) != -1)
  {
    switch(opt)
    {
      case 'h':
        course_proj.hours_wasted = atoi(optarg);
        break;
      case 'c':
        course_proj.completion_coeff = atof(optarg);
        break;
      case 'm':
        strcpy(course_proj.comment, optarg);
        break;
      case 'd':
        course_proj.coffee_drunk_ml = atoi(optarg);
        break;
      case 'f':
        course_proj.fastfood_eaten = atoi(optarg);
        break;
      case '?':
      default:
        printf("Usage: %s [-h hrs] [-m comment] [-c coeff] [-d ml] [-f kg].\n", argv[0]);
        return -1;
        break;
    }
  }
  print_data(&course_proj);

  return 0;
}