用c编程找出1000之内的所有完数，并按照下面格式输出其因子：6 its factors are 1，2，3

以下是用 C 语言编写的找出 1000 以内的所有完数的代码：

#include <stdio.h>

int main() {
    int i, j, sum;
    printf("Perfect numbers within 1000:\n");
    for (i = 1; i <= 1000; i++) {
        sum = 0;
        for (j = 1; j < i; j++) {
            if (i % j == 0) {
                sum += j;
            }
        }
        if (sum == i) {
            printf("%d its factors are ", i);
            for (j = 1; j < i; j++) {
                if (i % j == 0) {
                    printf("%d,", j);
                }
            }
            printf("\b are equal to %d\n", i);
        }
    }
    return 0;
}

输出结果如下：

Perfect numbers within 1000:
6 its factors are 1,2,3 are equal to 6
28 its factors are 1,2,4,7,14 are equal to 28
496 its factors are 1,2,4,8,16,31,62,124,248 are equal to 496

其中，完数指一个数恰好等于它的因子之和，例如 6 = 1 + 2 + 3。