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?

chqrlie · Accepted Answer · 2020-03-01 21:50:59Z

2

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;
}

edited Mar 1, 2020 at 21:50

answered Mar 1, 2020 at 17:00

chqrlie

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Comments

3CEZVQ · Accepted Answer · 2020-03-01 16:54:51Z

1

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);

edited Mar 1, 2020 at 16:54

answered Mar 1, 2020 at 16:48

3CEZVQ

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Comments

Eraklon · Accepted Answer · 2020-03-02 12:51:08Z

0

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;
}

edited Mar 2, 2020 at 12:51

answered Mar 1, 2020 at 16:54

Eraklon

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4 Comments

Zeuzif Over a year ago

i think that the answer is helpful, but the question is about to find conversion using recursive function !

Eraklon Over a year ago

"or a different approach entirely" From this I assumed he may interested in other approach also just to see one at least.

MiCo Over a year ago

Sorry, your implementation is wrong. I think, it only works correctly from 2 to 15. The first loop seems to be the reason. You are dealing with sizeof(int) which is not the number of bits. I would assume a factor CHAR_BITS from limits.h. for (i = sizeof(int)*CHAR_BIT - 1; i > 0 && (num & (1 << i)) == 0; i--); is better. And if (i != 0) is superfluos.

Eraklon Over a year ago

@MiCo Ohh, you are right. Good catch. Fixed it, thanks.

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