1309 - C语言程序设计教程（第三版）课后习题6.7
一个数如果恰好等于它的因子之和，这个数就称为"完数"。 例如，6的因子为1、2、3，而6=1+2+3，因此6是"完数"。 编程序找出N之内的所有完数，并按下面格式输出其因子：
Input
N
Output
? its factors are ? ? ?
Examples
Input
1000
Output
6 its factors are 1 2 3 28 its factors are 1 2 4 7 14 496 its factors are 1 2 4 8 16 31 62 124 248
Solution C++
#include<iostream> using namespace std; int main() { int n; cin>>n; for (int i=6; i<=n; i++) { int sum=0; for (int j=1; j<=i/2; j++) if (i%j==0) sum+=j; if (i==sum) { cout<<i<<" its factors are "; for (int j=1; j<=i/2; j++) if (i%j==0) cout<<j<<" "; cout<<endl; } } return 0; }