Thread: Need help

I need huge help. How do I Modify the program to print hex instead of binary, without using * printf("%x"). That is, use putchar() to output each hex digit.
* Note that putchar('0' + 1) outputs the character "1",
* putchar ('0' + 2) outputs the character "2", etc., and that
* putchar('a' + 1) outputs the letter "b",
* putchar('a' + 2) outputs the letter "c", etc.

Code:

int main(void) {
    printf("\n");
    print_binary(65535);
    print_binary(1<<31 | 1<<30 | 1<<5 | 1<<0);
    print_binary(-7);
    print_binary(-7.0);
    print_binary("42");
    printf("\n");
    return 0;
}


/*
 * Print num in binary, with leading zeros.
 */
void print_binary(int num) {
        // The current bit we're sending to output.  Remember,
        // the least significant bit is bit 0.
    int curr_bit_num = (sizeof(int) * 8 - 1);


    while (curr_bit_num >= 0) {
        int mask = 1 << curr_bit_num;
        int bit = ((mask & num) >> curr_bit_num) & 1;
        putchar('0' + bit);
        if (curr_bit_num > 0 && curr_bit_num % 4 == 0) {
            putchar('_');
        }
        curr_bit_num--;
    }


    printf("    is binary for %d\n", num);
}

Hex digits are 4 bit numbers, your job is to match each 4 bit number to its hex digit, and output a hex number based on an arbitrary set of bits. For example, 0101 is 5, 1110 is e, 0010 is 2 and 1010 is a. Together the set of bits 01011110101001010010 is 0x5ea52.

Thank you for the help