习题6-3 使用函数输出指定范围内的完数

#include<stdio.h>

int factorsum(int number);
void PrintPN(int m, int n);

int main(void)
{
    int m, n;

    scanf_s("%d %d", &m, &n);

    if (factorsum(m) == m)
    {
        printf("%d is a perfect number\n", m);
    }

    if (factorsum(n) == n)
    {
        printf("%d is a perfect number\n", n);
    }

    PrintPN(m, n);

    return 0;
}

int factorsum(int number)
{
    /*
        所有数都包含因数1，所以因数和的初值设为1，然后从2开始判断
    */
    int sum = 1;                            
    for (int i = 2; i < number; i++)
    {
        if (number % i == 0)
        {
            sum = sum + i;
        }
    }
    return sum;
}

void PrintPN(int m, int n)
{
    int flag = 0;
    for (int i = m; i <= n; i++)
    {
        if (factorsum(i) == i)
        {
            flag = 1;

            printf("%d = 1", i);
            for (int j = 2; j < i; j++)
            {
                if (i % j == 0)
                {
                    printf(" + %d", j);
                }                    
            }

            printf("\n");
        }
    }
    if (flag == 0)
    {
        printf("No perfect number\n");
    }
}