Iterating through digits in integer in C

Question

I have an integer like 1191223 and I want to iterate over the digits. I am not sure how to do this in C, is there any easy way to do this?

Thanks.

Answer 1

Forwards, or backwards?

Assuming a positive integer:

  unsigned int n = 1191223;

  while (n != 0) {
       doSomething (n % 10);
       n /= 10;
  }

…will work smallest to largest, or…

EDIT I'd forgotten all about this non-working solution I had here. Note that Very Smart People™ seem to use the smallest-to-largest iteration consistently (both Linux kernel and GLibC's printf, for example, just iterate backwards) but here's a lousy way to do it if you really don't want to use snprintf for some reason…

int left_to_right (unsigned int n) {
  unsigned int digit = 0;

  if (0 == n) {
    doSomething (0);
  } else {
    digit = pow(10, 1.0+ floor(log10(n)));
    while (digit /= 10) {
      doSomething ( (n / digit) % 10 );
    }
  }
}

I assume that it's very silly to assume that you have log10 and pow but not snprintf, so an alternate plan would be

int left_to_right_fixed_max (unsigned int n) {
  unsigned int digit = 1000000000; /* make this very big */
  unsigned int n10 = 10 * n;

  if (0 == n) {
    doSomething (0);
  } else {
    while (digit > n10) { digit /= 10; }
    while (digit /= 10) {
      doSomething ( (n / digit) % 10 );
    }
  }
}

… or, if you really don't have hardware multiply/divide, you can resort to using a table of powers of ten.

int left_to_right (unsigned int n) {
  static const unsigned int digit [] = 
    { 1,
      10,
      100,
      1000,
      10000,
      100000,
      1000000,
      10000000,
      100000000,
      1000000000 /* make this very big */
    };
  static const unsigned char max_place = 10;
  /* length of the above array */

  unsigned char decimal;
  unsigned char place;
  unsigned char significant = 0; /* boolean */

  if (0 == n) {
    doSomething (0);
  } else {
    place = max_place;
    while (place--) {
      decimal = 0;
      while (n >= digit[place]) {
        decimal++;
        n -= digit[place];
      }
      if (decimal | significant) {
        doSomething (decimal);
        significant |= decimal;
      }
    }
  }
}

…which I have adapted from http://www.piclist.com/techref/language/ccpp/convertbase.htm into a somewhat more general-purpose version.