#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define ONLY_ZERO_OR_ONE "Nur Null oder Eins eingeben\n"

char lowerCaseToUpperCase(char somechar)
{
  if (somechar == 'n' ||
      somechar == 'j')
  {
    somechar = somechar - 32;
  }
  return(somechar);
}

char checkDecision(char decision)
{
  int check = 0;

  while(check < 1)
  {
    if (decision != 'J' && decision != 'N')
    {
      printf("\a");
      printf("Nur n oder j eingeben!!\n");
      __fpurge(stdin);
      scanf ("%c", &decision);
      decision = lowerCaseToUpperCase(decision);
    }
    if (decision == 'J' || decision == 'N')
    {
      check = 1;
      return (decision);
    }
  }
  return(0);
}

char getDecision(char decision)
{
  printf("Wollen Sie noch eine Berechnung durchführen?\n");
  printf("j für Ja eingeben oder n für Nein eingeben\n");
  __fpurge(stdin);
  scanf ("%c", &decision);
  decision = lowerCaseToUpperCase(decision);
  return(decision);
}

void getBinary(int bin[5])
{
  int bin_counter = 0;

  while (bin_counter < 4)
  {
    if (bin_counter == 0)
    {
      printf("4 Binaer-Ziffern eingeben\n");
    }

    __fpurge(stdin);
    scanf ("%i", &bin[bin_counter]);

    if ( (bin[bin_counter] == 0) ||
         (bin[bin_counter] == 1))
    {
      bin_counter = bin_counter + 1;
    }

    if ( (bin[bin_counter] > 1) ||
         (bin[bin_counter] < 0) )
    {
      printf("\a");
      printf ("%s", ONLY_ZERO_OR_ONE);
    }
  }
}

int binaryToDecimal(int decimal, int bin[5])
{
  int ok_counter = 0;
  int pow_counter = 3;

  for (ok_counter = 0; ok_counter < 4;)
  {
    if (bin[ok_counter] == 1)
    {
      decimal = decimal + pow(2, pow_counter);
      ok_counter = ok_counter + 1;
      pow_counter = pow_counter - 1;
    }

    if (bin[ok_counter] == 0)
    {
      ok_counter = ok_counter + 1;
      pow_counter = pow_counter - 1;
    }
  }
  return(decimal);
}

int main()
{
  char decision = 'Y';
  int decimal = 0;
  int bin[5] = {};

  getBinary(bin);
  decimal = binaryToDecimal(decimal, bin);
  printf("Dezimal Zahl: %i\n", decimal);
  decision = getDecision(decision);
  decision = checkDecision(decision);

  if (decision == 'N')
  {
    return(0);
  }
  else
  {
    main();
  }

  return(0);
}