Number of Digit One

Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.

For example:
Given n = 13,
Return 6, because digit 1 occurred in the following numbers: 1, 10, 11, 12, 13.

Hint:

1. Beware of overflow.

 1 int countDigitOne(int n) {
 2     int count=0;
 3     long m=1;
 4     for(m=1;m<=n;m=m*10)
 5     {
 6         count+=(n/m+8)/10*m;
 7         if(n/m%10==1)
 8           count+=n%m+1;
 9     }
10     return count;
11 }