Question

I have to convert a decimal number to octal and hexadecimal using bitwise operations. I know how to convert it to binary:

char * decToBin(int n)
{
    unsigned int mask=128;
    char *converted;
    converted=(char *) malloc((log((double) mask)/log((double) 2))*sizeof(char)+2);
    strcpy(converted,"");

    while(mask > 0)
    {
        if(mask & n)
            strcat(converted,"1");
        else
            strcat(converted,"0");

        mask >>= 1;

    }

    return converted;
}  

May you help me convert from decimal to hexadecimal? What should the basic idea be? Is it possible to use a mask for that? Thank you.

Answer 1

You could “cheat” and use sprintf:

char *conv = calloc(1, sizeof(unsigned) * 2 + 3); // each byte is 2 characters in hex, and 2 characters for the 0x and 1 character for the trailing NUL
sprintf(conv, "0x%X", (unsigned) input);
return conv;

Or, to elaborate on @user1113426’s answer:

char *decToHex(unsigned input)
{
    char *output = malloc(sizeof(unsigned) * 2 + 3);
    strcpy(output, "0x00000000");

    static char HEX[] = "0123456789ABCDEF";

    // represents the end of the string.
    int index = 9;

    while (input > 0 ) {
        output[index--] = HEX[(input & 0xF)];
        input >>= 4;            
    }

    return output;
}