1.3闰年

方法一`

#include<stdio.h>
int main()
{
    int n;
    scanf("%d",&n);
    if(n%4==0)
    {
        if(n%100!=0)
            printf("%d is a leap year\n",n);
        else if(n%400==0)
            printf("%d is a leap year\n",n);
    }
    else printf("%d is not a leap year\n",n);
    return 0;
}

方法二

#include<stdio.h>
int main()
{
    int n;
    scanf("%d",&n);
    if((n%4==0)&&(n%100!=0)||n%400==0)
        printf("%d is a leap year\n",n);
    else printf("%d is not a leap year\n",n);
    return 0;
}

自动输出1900~2100年间的闰年

#include<stdio.h>
int main()
{
    int n;
    for(n=1900;n<=2100;n++)
    {
        if((n%4==0)&&(n%100!=0)||n%400==0)
        printf("%d is a leap year\n",n);
    }
    return 0;
}