Find the number of "1"

Question: Given a positive integer in decimal, write down all integers starting with 1, to N, and then count the number of "1" that appears.

First, try the numbers and then summarize the rules and finally program.

Code:

1#include <iostream>2 using namespacestd;3 4 intMain ()5 {6     inti;7     intN;8     inttemp;9     intnum =0;Ten  Onecout <<"cin a num:"; ACIN >>N; -      for(i =1; I <= N; i++) -     { thetemp =i; -          while(Temp! =0) -         { -             if(Temp%Ten==1) +             { -num++; +             } Atemp = temp/Ten; at         } -     } -cout << Num <<Endl; -}

Sentiment: The code is short but the algorithm, this kind of thinking is not easy. and the line and thinking ...

Find the number of "1"