Count total number of digits from 1 to n | C ++ program to count total number of digits we have to write from 1 to n ; number_of_digits store total digits we have to write ; In the loop we are decreasing 0 , 9 , 99 ... from n till ( n - i + 1 ) is greater than 0 and sum them to number_of_digits to get the required sum ; Driver code
#include <bits/stdc++.h> NEW_LINE using namespace std ; int totalDigits ( int n ) { int number_of_digits = 0 ; for ( int i = 1 ; i <= n ; i *= 10 ) number_of_digits += ( n - i + 1 ) ; return number_of_digits ; } int main ( ) { int n = 13 ; cout << totalDigits ( n ) << endl ; return 0 ; }