#include <iomanip> #include <iostream> using namespace std; int main() { // write your code here...... long long sum = 0; int i = 0; double k = 10; while(i < 10) { sum+=(k - 1); k*= 10; i++; } cout << sum << endl; return 0; } 题目中不难发现,9 = 10 - 1; 99 = 100 - 1;999 = 1000 - 1...