帮我用c语言使用51单片机写一个万年历代码

好的，您需要一个万年历的代码，使用C语言和51单片机来编写。以下是一个简单的示例代码，可以满足您的要求。

#include <reg51.h>

unsigned char code month_days[12] = {31,28,31,30,31,30,31,31,30,31,30,31}; //每个月的天数
unsigned char code week_days[7] = {"Sun Mon Tue Wed Thu Fri Sat"}; //一周的天数

void delay(unsigned int time); //延时函数
void lcd_init(void); //初始化液晶屏
void lcd_clear(void); //清楚液晶屏
void lcd_write_command(unsigned char command); //写指令
void lcd_write_data(unsigned char data1); //写数据
void show_date(unsigned char week, unsigned char month, unsigned char day); //显示日期

void main()
{
    unsigned char week = 0, month = 1, day = 1; //初始化为周一
    unsigned char year = 21; //当前年份
    unsigned char key;
    lcd_init(); //初始化液晶屏
    while(1)
    {
        //显示日期
        show_date(week, month, day);
        //获取按键值
        key = P1;
        //按键控制年月日
        if(key == 0xfe) //上一年
        {
            year--;
            if(year < 21) year = 99;
            delay(500);
        }
        else if(key == 0xfd) //下一年
        {
            year++;
            if(year > 99) year = 21;
            delay(500);
        }
        else if(key == 0xfb) //上一月
        {
            month--;
            if(month == 0) month = 12;
            day = 1;
            if(month == 2 && year%4 == 0)
                month_days[1] = 29;
            else
                month_days[1] = 28;
            week--;
            if(week == -1) week = 6;
            delay(500);
        }
        else if(key == 0xf7) //下一月
        {
            month++;
            if(month > 12) month = 1;
            day = 1;
            if(month == 2 && year%4 == 0)
                month_days[1] = 29;
            else
                month_days[1] = 28;
            week++;
            if(week == 7) week = 0;
            delay(500);
        }
        else if(key == 0xef) //上一日
        {
            day--;
            if(day == 0)
            {
                month--;
                if(month == 0) month = 12;
                day = month_days[month-1];
                if(month == 2 && year%4 == 0)
                    month_days[1] = 29;
                else
                    month_days[1] = 28;
            }
            week--;
            if(week == -1) week = 6;
            delay(50);
        }
        else if(key == 0xdf) //下一日
        {
            day++;
            if(day > month_days[month-1])
            {
                month++;
                if(month > 12) month = 1;
                day = 1;
                if(month == 2 && year%4 == 0)
                    month_days[1] = 29;
                else
                    month_days[1] = 28;
            }
            week++;
            if(week == 7) week = 0;
            delay(50);
        }
        else //不操作
        {
            delay(50);
        }
        //清屏
        lcd_clear();
    }
}

//延时函数
void delay(unsigned int time)
{
    unsigned int i,j;
    for(i = 0;i < time;i++)
        for(j = 0;j < 125;j++);
}

//初始化液晶屏
void lcd_init(void)
{
    lcd_write_command(0x38); //设置显示模式
    delay(20);
    lcd_write_command(0x0c); //显示开关控制
    delay(20);
    lcd_write_command(0x06); //设置输入模式
    delay(20);
    lcd_write_command(0x01); //清屏，指针回到起点
    delay(20);
}

//清楚液晶屏
void lcd_clear(void)
{
    lcd_write_command(0x01); //清屏，指针回到起点
    delay(20);
}

//写指令
void lcd_write_command(unsigned char command)
{
    P2 = command;
    P3 &= ~(0x01);
    P3 |= 0x02;
    delay(5);
    P3 &= ~(0x02);
}

//写数据
void lcd_write_data(unsigned char data1)
{
    P2 = data1;
    P3 |= 0x01;
    P3 |= 0x02;
    delay(5);
    P3 &= ~(0x02);
}

//显示日期
void show_date(unsigned char week, unsigned char month, unsigned char day)
{
    unsigned char w = week;
    lcd_write_data(year/10+'0');
    lcd_write_data(year%10+'0');
    lcd_write_data('/');
    lcd_write_data(month/10+'0');
    lcd_write_data(month%10+'0');
    lcd_write_data('/');
    lcd_write_data(day/10+'0');
    lcd_write_data(day%10+'0');
    lcd_write_data(' ');
    while(w--)
        lcd_write_data(' ');
    lcd_write_data(week_days+(week*4));
}

这段代码使用了51单片机和液晶屏来实现一个简单的万年历，可以通过上下左右键来控制年、月、日，显示当前日期。需要注意的是，该代码只是一个示例，可能存在一些错误，您需要针对自己的需求进行修改完善。