Can putchar() print an integer?

Question

How can I print an integer with the help of putchar() only. i want to do it without using external storage.
This question was asked in an interview last year.

Answer 1

When faced with vague requirements on an interview, it's a good idea to express your assumptions.

I would take the requirement about only being able to use putchar to mean that it is the only library function I am allowed to call. I would furthermore assume that "no external storage" meant that I could not explicitly create a buffer. If the interviewer agreed with my assumptions, I would proceed with:

void pr_int(int n) {
    if (n < 0) {
        putchar('-');
        n = -n;
    }
    if (n / 10 != 0)
        pr_int(n / 10);
    putchar((n % 10) + '0');
}

If the interviewer then commented that n = -n; would fail for INT_MIN, as noted below, then I would rewrite it as:

void pr_uint(unsigned int n) {
    if (n / 10 != 0)
        pr_uint(n / 10);
    putchar((n % 10) + '0');
}

void pr_int(int n) {
    if (n < 0) {
        putchar('-');
        n = -n;
    }
    pr_uint((unsigned int) n);
}