// Convert a decimal integer do a binary string
// added a test printf() you can remove later
// Turbo C modified for Pelles C     vegaseat    19nov2004
 
#include <stdio.h>
 
void dec2bin(long decimal, char *binary);
 
int main()
{
  long decimal;
  char binary[80];
 
  printf("\n\n Enter an integer value : ");
  scanf("%ld",&decimal);
  dec2bin(decimal,binary);
  printf("\n The binary value of %ld is %s \n",decimal,binary);
 
  getchar();  // trap enter 
  getchar();  // wait
  return 0;
}
 
//
// accepts a decimal integer and returns a binary coded string
//
void dec2bin(long decimal, char *binary)
{
  int  k = 0, n = 0;
  int  neg_flag = 0;
  int  remain;
  int  old_decimal;  // for test
  char temp[80];
 
  // take care of negative input
  if (decimal < 0)
  {      
    decimal = -decimal;
    neg_flag = 1;
  }
  do 
  {
    old_decimal = decimal;   // for test
    remain    = decimal % 2;
    // whittle down the decimal number
    decimal   = decimal / 2;
    // this is a test to show the action
    printf("%d/2 = %d  remainder = %d\n", old_decimal, decimal, remain);
    // converts digit 0 or 1 to character '0' or '1'
    temp[k++] = remain + '0';
  } while (decimal > 0);
 
  if (neg_flag)
    temp[k++] = '-';       // add - sign
  else
    temp[k++] = ' ';       // space
 
  // reverse the spelling
  while (k >= 0)
    binary[n++] = temp[--k];
 
  binary[n-1] = 0;         // end with NULL
}