Converting int to binary String in C

Question

I'm trying to convert an integer to a binary String (see code below). I've already looked at several similar code snippets, and can't seem to find the reason as to why this does not work. It not only doesn't produce the correct output, but no output at all. Can somebody please explain to me in detail what I'm doing wrong?

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

char* toBinaryString(int n) {
  char *string = malloc(sizeof(int) * 8 + 1);
  if (!string) {
    return NULL;
  }
  for (int i = 31; i >= 0; i--) {
    string[i] = n & 1;
    n >> 1;
  }
  return string;
}

int main() {
  char* string = toBinaryString(4);
  printf("%s", string);
  free(string);
  return 0;
}

@JohnnyMopp How would I do that? Can I just write string[32] = '\0'? — RalphBear
– RalphBear, Commented Jun 21, 2021 at 14:04
@EugeneSh. If I change it to n = n >> 1, that still doesn't change the output. — RalphBear
– RalphBear, Commented Jun 21, 2021 at 14:05

MikeCAT · Accepted Answer · 2021-06-21 14:07:01Z

4

The line

string[i] = n & 1;

is assigning integers 0 or 1 to string[i]. They are typically different from the characters '0' and '1'. You should add '0' to convert the integers to characters.

Also, as @EugeneSh. pointed out, the line

n >> 1;

has no effect. It should be

n >>= 1;

to update the n's value.

Also, as @JohnnyMopp pointed out, you should terminate the string by adding a null-character.

One more point it that you should check if malloc() succeeded. (It is done in the function toBinaryString, but there is no check in main() before printing its result)

Finally, It doesn't looks so good to use a magic number 31 for the initialization of for loop while using sizeof(int) for the size for malloc().

Fixed code:

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

char* toBinaryString(int n) {
  int num_bits = sizeof(int) * 8;
  char *string = malloc(num_bits + 1);
  if (!string) {
    return NULL;
  }
  for (int i = num_bits - 1; i >= 0; i--) {
    string[i] = (n & 1) + '0';
    n >>= 1;
  }
  string[num_bits] = '\0';
  return string;
}

int main() {
  char* string = toBinaryString(4);
  if (string) {
    printf("%s", string);
    free(string);
  } else {
    fputs("toBinaryString() failed\n", stderr);
  }
  return 0;
}

answered Jun 21, 2021 at 14:07

MikeCAT

75.1k11 gold badges50 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

MikeCAT Over a year ago

@chux-ReinstateMonica Thank you for pointing out. I'll fix.

RalphBear Over a year ago

Would casting the result of n & 1 to char have the same effect as adding '0' as you did here?

MikeCAT Over a year ago

@RalphBear No. Casting won't change the value unless the old value doesn't fit in the range of the new type.

SGeorgiades · Accepted Answer · 2021-06-21 14:11:28Z

1

The values you are putting into the string are either a binary zero or a binary one, when what you want is the digit 0 or the digit one. Try string[i] = (n & 1) + '0';. Binary 0 and 1 are non-printing characters, so that's why you get no output.

answered Jun 21, 2021 at 14:11

SGeorgiades

1,8311 gold badge12 silver badges11 bronze badges

2 Comments

MikeCAT Over a year ago

There are no output not just because 0 and 1 are non-printing characters. The first element in the array will be 0, and 0 is used as a string terminator, so actually there will be no output even when it is seen as binary.

SGeorgiades Over a year ago

Yes, very true @MikeCAT

blablablabla · Accepted Answer · 2021-09-06 19:34:08Z

1

#define INT_WIDTH 32
#define TEST 1

char *IntToBin(unsigned x, char *buffer) {
    char *ptr = buffer + INT_WIDTH;
    do {
        *(--ptr) = '0' + (x & 1);
        x >>= 1;
    } while(x);
    return ptr;
}

#if TEST
    #include <stdio.h>

    int main() {
        int n;
        char str[INT_WIDTH+1]; str[INT_WIDTH]='\0';
        while(scanf("%d", &n) == 1)
            puts(IntToBin(n, str));
        return 0;   
    }
#endif

answered Sep 6, 2021 at 19:34

blablablabla

333 bronze badges

1 Comment

Community Over a year ago

Please add further details to expand on your answer, such as working code or documentation citations.

Collectives™ on Stack Overflow

Converting int to binary String in C

3 Answers 3

3 Comments

2 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related