为什么调用函数，执行了两次？

#define _CRT_SECURE_NO_WARNINGS
#include 
int yearIn(int year);//输入
int run_year(int year);//判断
int printyear(int year);
    int main()
    {   
        int year = 0;
        printyear(year);
        return 0;
    }

    int yearIn(int year) {
        printf("请输入年份:\n");
        scanf("%d", &year);
        return year;
    }

    int run_year(int year) {
        int a;
        int b;
        b = yearIn(year);
        if (b % 400 == 0)
            a = 1;
        else
        {
            if (b % 4 == 0 && b % 100 != 0)
                a = 1;
            else
                a = 0;
        }
        return a;
    }

    int printyear(int year) {
        if (run_year(year) == 1)
        {
            printf("%d年是闰年\n",yearIn(year));
        }
        else
        {
            printf("%d年非闰年\n", yearIn(year));
        }
        return 0;
    }

在 printyear 函数中，你调用了 yearIn 函数两次，导致输入了两次年份。你可以将 yearIn 函数的调用移到 main 函数中，将输入的年份传给 printyear 函数。修改后的代码如下：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int yearIn(int year); // 输入
int run_year(int year); // 判断
int printyear(int year);

int main()
{
    int year = 0;
    printf("请输入年份:\n");
    scanf("%d", &year);
    printyear(year);
    return 0;
}

int yearIn(int year)
{
    return year;
}

int run_year(int year)
{
    int a;
    if (year % 400 == 0)
        a = 1;
    else
    {
        if (year % 4 == 0 && year % 100 != 0)
            a = 1;
        else
            a = 0;
    }
    return a;
}

int printyear(int year)
{
    if (run_year(year) == 1)
    {
        printf("%d年是闰年\n", year);
    }
    else
    {
        printf("%d年非闰年\n", year);
    }
    return 0;
}

这样在 printyear 函数中就不会再调用 yearIn 函数了，就不会再输入年份两次。