今天自己写了两款软件，拿出来给大家看看，刚学c语言没多久，希望大家点评点评。懂行的看门道，行外的看热闹。
判断闰年：
#include "stdio.h"
void main()
{
    int year,mod1,mod2,mod3;
    printf("please type a year number.\n");
    scanf("%d",&year);
    mod1=year%4;
    mod2=year%100;
    mod3=year%400;
    if (mod1==0)
        {
        if (mod2==0)
            {
            if (mod3==0)
            {
            printf("this number is runnian.\n");
            }
            else
            {
            printf("this year is not runnian.\n");
            }
            }
        else
        {
        printf("the year is runnian.\n");
        }
        }
    else
        {
        printf("the year is not a runian.\n");
        }
        
}
输出任意数内的所有素数
#include "stdio.h"
void main()
{
    void qiushusu(int j);
    int n,number;
    scanf("%d",&number);
    for(n=2;n<=(number-1);n++)
    {
        qiushusu(n);
    }
}
void qiushusu(int j)
{
int i,mod,a;
a=0;
for (i=2;i<=(j-1);i++)
    {
    mod=j%i;
    if (mod==0)
        {
        a=a+1;
        }
    }
if (a==0)
    printf("%d\n",j);
}

为什么是
return i >= n; //可以表示成return i == n;
这和那个if判断有什么关系