How can I count the digits in an integer without a string cast?

Question

I fear there\'s a simple and obvious answer to this question. I need to determine how many digits wide a count of items is, so that I can pad each item number with the m

Answer 1

A more efficient solution than repeated division would be repeated if statements with multiplies... e.g. (where n is the number whose number of digits is required)

unsigned int test = 1;
unsigned int digits = 0;
while (n >= test)
{
  ++digits;
  test *= 10;
}

If there is some reasonable upper bound on the item count (e.g. the 32-bit range of an unsigned int) then an even better way is to compare with members of some static array, e.g.

// this covers the whole range of 32-bit unsigned values
const unsigned int test[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };

unsigned int digits = 10;
while(n < test[digits]) --digits;