store binary of decimal in char array

Question

I want to store binary equivalent of decimal number in char array by applying below code, but the problem is I am not able to hold the last bit of the decimal number. I am getting garbage values.

 int k,j;
 char c[40];
 j=32;
 scanf("%d",&k);

 while(k)
 {    
     k=k>>1;
     c[j]=k|1;
     j--;
 }

 puts("number is");
 puts(c);

Answer 1

Besides the problems noted by @SouravGhosh, you need to

(5) convert from the digits 0/1 to the character values for '0' and '1' by adding in the value of the character '0' [actually Sourav noted that too], and

(6) pick off the low-order bit before shifting k right by 1 bit.

Here's a working version:

char c[40];
int j=39;
c[j--]='\0';
while(k)
    {
    c[j]=(k&1)+'0';
    j--;
    k=k>>1;
    }

puts("number is ");
puts(&c[j+1]);

Answer 2

If interested, here is a slightly different method...

Consider that for a graphical binary representation of a 32 bit integer, you would need to contain 33 bytes: 32 for 1s and 0s, and 1 for string NULL terminator. As you walk through any 32 bit representation of an integer value, you can logical and (&) the corresponding bit of 2^32 (2147483648) with each bit position of your input integer value to determine if that position should be a "1" or a "0", stacking the resultant character (ASCII) representations of 1 or 0 (48 or 49) as you go, into a string.

Here is the example to convert an integer into a 32 bit binary representation...

const char *byte_to_binary32(long x)
{
    static char b[33]; // bits plus '\0'
    b[0] = '\0';
    char *p = b;  
    //unsigned long long z; required only if 64 bit conversion
    unsigned long z;//this is sufficient for 32 bit conversion
    for (z = 2147483648; z > 0; z >>= 1)       //2^32
    {
        *p++ = (x & z) ? '1' : '0';
    }
    return b;
}

int main(void)
{
    printf("Binary: %s\n\n", byte_to_binary32(100));
    return 0;
}

Answer 3

I assume you want the lexicographical representation for the binary.

You need to take care of few things.

1. You must initialize k before using. Ask for user input (or "hardcode", as we say) the value for k.

2. If you want to use array c as string, you need to null-terminate it.

3. You need to perform & with a value of 1 to take out the last bit. Add that with '0' (Remember, lexicographical). Store that.

4. Current array indexing will put you into trouble. You can use normal array indexing with j, starting from 0. After the loop, you need to null-terminate the last index and then go for printing.

A pseudo-code will look like

#include <stdio.h>

int main(void) {

    int val = 16;
    char  bin [128] = {0};
    int index = 0;

    while(val)
    {
        bin[index] = '0' + (val&1u);
        val = val >> 1;
        index++;
    }
    bin[index] = 0;

    puts(bin);


    return 0;
}

SEE A LIVE DEMO

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^{NOTE: You may want to reverse the string before printing it.}