C语言计算分段函数

/*
革启博客，程序袁欢，袁欢的博客，袁欢博客
版本：vs2019社区版
功能：计算分段函数*/
#include<stdio.h>
double factorial(int a)
{
    int i;
    double factorial_Value = 1.0;
    for (i = 1; i < a; i++)
    {
        factorial_Value = factorial_Value * i;
    }
    return factorial_Value;
}
void main()
{
    int m = 0, n = 0;
    double factorial_m = 0;
    double factorial_n = 0;
    double factorial_mn = 0;
    double P_mn = 0.0;
    printf("请输入两个参数的值：\n");
    printf("m=");
    scanf_s("%d", &m);
    printf("n=");
    scanf_s("%d", &n);
    if (m > n)
    {
        factorial_m = factorial(m);
        factorial_n = factorial(n);
        factorial_mn = factorial(m - n);
        if (0 == factorial_n || 0 == factorial_mn)
        {
            printf("错误，0不能作为除数！\n");
        }
        else
        {
            P_mn = factorial_m / (factorial_n * factorial_mn);
        }
    }
    else
    {
        P_mn = 0;
    }
    printf("计算结果为：");
    printf("P_mn=%f\n", P_mn);
}