Converting an integer to binary in C

Question

I\'m trying to convert an integer 10 into the binary number 1010.

This code attempts it, but I get a segfault on the strcat():

int int_to_bin(int k)
{
          


        

Answer 1

You can add the functions to the standard library and use it whenever you need.

Here is the code in C++

#include <stdio.h>

int power(int x, int y) //calculates x^y.
{
int product = 1;
for (int i = 0; i < y; i++)
{
    product = product * x;
}
return (product);
}
int gpow_bin(int a) //highest power of 2 less/equal to than number itself.
{
int i, z, t;
for (i = 0;; i++)
{
    t = power(2, i);
    z = a / t;
    if (z == 0)
    {
        break;
    }
}
return (i - 1);
}
void bin_write(int x)
{
//printf("%d", 1);
int current_power = gpow_bin(x);
int left = x - power(2, current_power);
int lower_power = gpow_bin(left);
for (int i = 1; i < current_power - lower_power; i++)
{
    printf("0");
}
if (left != 0)
{
    printf("%d", 1);
    bin_write(left);
}
}
void main()
{
//printf("%d", gpow_bin(67));
int user_input;
printf("Give the input:: ");
scanf("%d", &user_input);
printf("%d", 1);
bin_write(user_input);
}

Answer 2

You need to initialise bin, e.g.

bin = malloc(1);
bin[0] = '\0';

or use calloc:

bin = calloc(1, 1);

You also have a bug here:

 bin = (char *)realloc(bin, sizeof(char) * (sizeof(bin)+1));

this needs to be:

 bin = (char *)realloc(bin, sizeof(char) * (strlen(bin)+1));

(i.e. use strlen, not sizeof).

And you should increase the size before calling strcat.

And you're not freeing bin, so you have a memory leak.

And you need to convert 0, 1 to '0', '1'.

And you can't strcat a char to a string.

So apart from that, it's close, but the code should probably be more like this (warning, untested !):

int int_to_bin(int k)
{
   char *bin;
   int tmp;

   bin = calloc(1, 1);
   while (k > 0)
   {
      bin = realloc(bin, strlen(bin) + 2);
      bin[strlen(bin) - 1] = (k % 2) + '0';
      bin[strlen(bin)] = '\0';
      k = k / 2;
   }
   tmp = atoi(bin);
   free(bin);
   return tmp;
}

Answer 3

You can use function this function to return char* with string representation of the integer:

   char* itob(int i) {
      static char bits[8] = {'0','0','0','0','0','0','0','0'};
      int bits_index = 7;
      while ( i > 0 ) {
         bits[bits_index--] = (i & 1) + '0';
         i = ( i >> 1);
      }
      return bits;
   }

It's not a perfect implementation, but if you test with a simple printf("%s", itob(170)), you'll get 01010101 as I recall 170 was. Add atoi(itob(170)) and you'll get the integer but it's definitely not 170 in integer value.

Answer 4

short a;
short b;
short c;
short d;
short e;
short f;
short g;
short h;
int i;
char j[256];

printf("BINARY CONVERTER\n\n\n");

//uses <stdlib.h>

while(1)
{

a=0;
b=0;
c=0;
d=0;
e=0;
f=0;
g=0;
h=0;
i=0;


gets(j);
i=atoi(j);
if(i>255){
printf("int i must not pass the value 255.\n");
i=0;
}
if(i>=128){
a=1;
i=i-128;}
if(i>=64){
b=1;
i=i-64;}
if(i>=32){
c=1;
i=i-32;}
if(i>=16){
d=1;
i=i-16;}
if(i>=8){
e=1;
i=i-8;}
if(i>=4){
f=1;
i=i-4;}
if(i>=2){
g=1;
i=i-2;}
if(i>=1){
h=1;
i=i-1;}

printf("\n%d%d%d%d%d%d%d%d\n\n",a,b,c,d,e,f,g,h);
}

Answer 5

Well, I had the same trouble ... so I found this thread

I think the answer from user:"pmg" does not work always.

unsigned int int_to_int(unsigned int k) {
    return (k == 0 || k == 1 ? k : ((k % 2) + 10 * int_to_int(k / 2)));
}

Reason: the binary representation is stored as an integer. That is quite limited. Imagine converting a decimal to binary:

 dec 255  -> hex 0xFF  -> bin 0b1111_1111
 dec 1023 -> hex 0x3FF -> bin 0b11_1111_1111

and you have to store this binary representation as it were a decimal number.

I think the solution from Andy Finkenstadt is the closest to what you need

unsigned int_to_int(unsigned int k) {
    char buffer[65]; // any number higher than sizeof(unsigned int)*bits_per_byte(8)
    return itoa( atoi(k, buffer, 2) );
}

but still this does not work for large numbers. No suprise, since you probably don't really need to convert the string back to decimal. It makes less sense. If you need a binary number usually you need for a text somewhere, so leave it in string format.

simply use itoa()

char buffer[65];
itoa(k, buffer, 2);

Answer 6

Just use itoa to convert to a string, then use atoi to convert back to decimal.

unsigned int_to_int(unsigned int k) {
    char buffer[65]; /* any number higher than sizeof(unsigned int)*bits_per_byte(8) */
    return atoi( itoa(k, buffer, 2) );
}