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#include <iostream> using namespace std; unsigned int tongji(int m); unsigned int numOfone(unsigned int n); void main() { unsigned int i(0); cout << "Please input the number for calculate:"; cin >> i; cout << tongji(i) << endl; } unsigned int tongji(int m) { if (m == 1) { return 1; } else { return tongji(m - 1) + numOfone(m); } } unsigned int numOfone(unsigned int n) { unsigned int count = 0; if (n / 10000 == 1) { count ++; } n %= 10000; if (n / 1000 == 1) { count ++; } n %= 1000; if (n / 100 == 1) { count ++; } n %= 100; if (n / 10 == 1) { count ++; } n %= 10; if (n / 1 == 1) { count ++; } return count; } // 5  =>  1 ;  13  =>  6

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