今天参考网上各路大神代码，然后自己利用思路打了一遍

#include<stdio.h>

#define MONTHS 12

int runnian_day(int,int,int);
int is_runnian(int);
int get_days(int, int, int);                                                            //返回从公元元年算起，某年某月某日是第几天， 用这个数字算星期几 
int days_of_year(int, int, int);                                                        //返回某年某月某日是当前年份第几天
int days_of_month(int, int);                                                            //返还某年某月有几天
void whichday(int,int,int);
void print_last(int,int,int);

int main(){
	int i,j,k;
	printf("请输入年月日(格式为2000/2/22)：");
	scanf("%d/%d/%d",&i,&j,&k);
	print_last(i,j,k);
}

int runnian_day(int a,int b,int c){
	int sum = 0;
	int i;
	for(i=1;i<=a-1;i++){
		if(is_runnian(i)){
			sum ++;
		}
	}
	return sum;
	
}

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

//返回这一天从公元元年算起是第几天,算法：1.先算整年的部分：比如2018年，完整已经过了的年份有2017个，按平年算有 2017 * 365 天，但是其中闰年是366天，每个闰年少算了一天。1至2017有几个闰年呢
 int get_days(int year, int month, int day)
{
    int days = days_of_year(year, month, day);
    int temp = year-1;
    return temp * 365 + runnian_day(year,month,day) +  days;
}
 
 

 //返回这一天在当年是第几天 
int days_of_year(int year, int month, int day)
{
     int i;
     int days = 0;
     for(i = 1; i < month; i++)
     {
         days += days_of_month(year, i);
         
     }
     return days + day;
}

//返回这个月一共有多少天 
int days_of_month(int year, int month)
{
    //存储平年每月的天数 
    const int  month_days[MONTHS] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    if(month ==2 && is_runnian(year))
        return 29; // 如果是闰年2月，返回29天 
    else
        return month_days[month-1];  //正常返回 
}

void whichday(int a,int b,int c){
	int temp = get_days(a,b,c)%7;
	printf("   今天是星期");
	switch(temp){
		case 0:puts("日");break;
		case 1:puts("一");break;
		case 2:puts("二");break;
		case 3:puts("三");break;
		case 4:puts("四");break;
		case 5:puts("五");break;
		case 6:puts("六");break;
	}
	puts("");puts("");puts("");puts("");puts("");
	system("pause");
}

void print_last(int a,int b,int c){
	int firstday_of_tmonth = get_days(a, b, 1) % 7;
	int tmonth_days = days_of_month(a, b);  //这个月一共多少天 
	int i,j;
	puts("");puts("");puts("");
	printf("               ");
    switch(b)
    {
        case 1: printf("January\n");    break;
        case 2: printf("February\n");    break;
        case 3: printf("March\n");    break;
        case 4: printf("April\n");    break;
        case 5: printf("May\n");    break;
        case 6: printf("June\n");    break;
        case 7: printf("July\n");    break;
        case 8: printf("August\n");    break;
        case 9: printf("September\n");    break;
        case 10: printf("October\n");    break;
        case 11: printf("November\n");    break;
        case 12: printf("December\n");    break;
        default: printf("Bad input of month, please enter a right month.\n"); return;
    }
    puts("   Mon   Tues   Wed  Thur   Fri  Sat   Sun");
    
    for(i=1;i<=tmonth_days;i++){
    	if(i==1){
    //先打印第一天的位置 
    			for(j = 1; j < firstday_of_tmonth; j++) {
        		printf("      ");
    			}
  		  printf("%6d", 1);
     //如果今天是星期日，换行
   				 if(firstday_of_tmonth == 7)
        			 printf("\n");
        			 continue;
		}
    	printf("%6d", i);
    	if(((firstday_of_tmonth+i-1)%7 == 0)||(i==tmonth_days)){
    		puts("");
		}
	}
	whichday(a,b,c);
}