C语言实现根据日期计算星期几的代码详解

#include"stdio.h"
void main()
{long i=1,run=0,ping=0,j,k,total;
int year,month,day;
printf("please enter year month day\n");
scanf("%d%d%d",&year,&month,&day);/*数据用空格或回车分开*/
printf("%d,%d,%d\n",year,month,day);
while(i<year)
 {
   {if((i%4==0&&i%100!=0)||(i%400==0))
      run++;
    else ping++;
   };
  i++;
 /*printf("%d\n",i-ping-1);此句可反映这年前，有多少个润年*/
  };
 j=run*366+ping*365;
 if((year%4==0&&year%100!=0)||(year%400==0))
   {switch(month)
     {case  1:k=day;break;
      case  2:k=day+31;break;
  case  3:k=day+31+29;break;
      case  4:k=day+31+29+31;break;
  case  5:k=day+31+29+31+30;break;
  case  6:k=day+31+29+31+30+31;break;
  case  7:k=day+31+29+31+30+31+30;break;
  case  8:k=day+31+29+31+30+31+30+31;break;
  case  9:k=day+31+29+31+30+31+30+31+31;break;
  case 10:k=day+31+29+31+30+31+30+31+31+30;break;
  case 11:k=day+31+29+31+30+31+30+31+31+30+31;break;