decimal to binary conversion using recursive functions

Question

I have an assignment to convert a number from decimal to binary. My problem is that I need to have it printed out directly from the function, instead of returning it back to main. Due to this, my printed out code is in the wrong order. (ex: for 6, my code prints out 011 instead of 110 )

This is what I have been using for the function:

int printBinary(int integer) {
    int remainder;

    if (integer < 1) {
        return 0;
    } else {
        remainder = integer % 2;
        printf("%d", remainder);
        integer = integer / 2;
        printBinary(integer);
        return 0;
    }
}

Does anyone have a suggestion on how I can print it out in reverse, or a different approach entirely?

Answer 1

You should just print the digit after the recursive call that prints the higher order bits.

Note also that your function prints nothing for 0 , which is probably incorrect.

Here is a simplified version:

int printBinary(int integer) {
    if (integer > 1)
        printBinary(integer / 2);
    printf("%d", integer % 2);
    return 0;
}

Answer 2

Your function prints binary digits starting from the tail. Just change the order of recursive call and printf.

int printBinary(int integer)  {

    int remainder;
    if (integer < 1)  {
    return 0;
    }
    else  {
        printBinary(integer / 2);
        remainder = integer % 2;
        printf("%d", remainder);
    return 0;
    }
}

It was

printBinary(6);
printf("%d", 0);
printBinary(3);
printf("%d", 1);
printBinary(1);
printf("%d", 1);
printBinary(0);

It is now

printBinary(6);
printBinary(3);
printBinary(1);
printBinary(0);
printf("%d", 1);
printf("%d", 1);
printf("%d", 0);

Answer 3

Also you could try something like this

#include <stdio.h>
#include <limits.h>

void printBinary(int num) {
  int i;

  // findind the first non 0 binary position from MSB
  for (i = sizeof(int) * CHAR_BIT - 1; i >= 0 && (num & (1 << i)) == 0; i--);

  for (; i >= 0; i--) // start the printing from here, so trailing 0's avoided
    if ((num & (1 << i)) == 0)
      printf("0");
    else
      printf("1");
}

int main() 
{
    printBinary(6);
    return 0;
}