C语言的一道题 知道1900年1月1日是星期一，设计一个程序，输入年月日，输出星期几

Question

#include "stdio.h"
int main(void)
{
int a,b,year,month,day,count=0;
printf("Please input year month day like this xxxx,xx,xx\n");
scanf("%d,%,d,%d",&year,&month,&day);
for(a=1901;a<=year;a++)
{ if(a%100!=0&&a%4==0)
count+=366;
else
if(a%400==0)
count+=366;
else
count+=365;
}
b=count%7;
switch(b)
{
case 0:
printf("The day is Monday\n");
break;
case 1:
printf("The day is Tuesday\n");
break;
case 2:
printf("The day is Wednesday\n");
break;
case 3:
printf("The day is Thursday\n");
break;
case 4:
printf("The day is Friday\n");
break;
case 5:
printf("The day is Satday\n");
break;
case 6:
printf("The day is Sunday\n");
break;
}
}
这是我自己设计到一半的程序，不知道怎么加入一个计算天数的程序。
我是这样想的如果我输入的是2017，03，21 但是我的程序只能算到2017，01，01
后面的天数要怎么加上去

Answer 1

#include "stdio.h"

int main(void)

{

int a,b,year,month,day,count=0;

int mon[12]={0,31,28,31,30,31,30,31,31,30,31,30};

printf("Please input year month day like this xxxx,xx,xx\n");

scanf("%d,%d,%d",&year,&month,&day);

for(a=1900;a<year;a++)

if(a%100!=0&&a%4==0||a%400==0)

count+=2;

else

count+=1;

for(a=1;a<month;a++)

{count+=mon[a];

if(a==2&&year%100!=0&&year%4==0||year%400==0)

count++;

}

count+=day;

b=count%7;

switch(b)

{

case 1:

printf("The day is Monday\n");

break;

case 2:

printf("The day is Tuesday\n");

break;

case 3:

printf("The day is Wednesday\n");

break;

case 4:

printf("The day is Thursday\n");

break;

case 5:

printf("The day is Friday\n");

break;

case 6:

printf("The day is Satday\n");

break;

case 0:

printf("The day is Sunday\n");

break;

}

}