C语言题目5

//用C语言编写程序：今天是2012年4月12日星期四，编写程序，
//输入今天开始到12月31日之间的任意日期，输出那一天是星期几。
#include"stdio.h"
int getdays(int month, int day)
{
  int months[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
  int i = 0;
  int days = 0;
  month = month-1;
  if(month>11)
   {
     printf("月份%d过大，请输入合法的日期！", month+1);
     return -1;
   }
  for(i=0; i<12; i++)
    {
      if(i!=month)
	{
	  days = days+months[i];
	}
      else
	{
	  if(day > months[i])
	    {
	      printf("日期%d过大，请输入合法的日期！", day);
	      return -1;
	    }
	  days = days+day;
	  break;
	}
    }
  return days;
}
int main()
{
  int x;
  int start;
  int end;
  int endmonth;
  int endday;
  int dayspan;
  int weekday;
  int startweekday;
  int result;
  char week[7][10]={{'M','o','n','d','a','y','\0'},
		   {'T','u','e','s','d','a','y','\0'},
		   {'W','e','d','n','e','s','d','a','y','\0'},
		   {'T','h','u','r','s','d','a','y','\0'},
		   {'F','r','i','d','a','y','\0'},
		   {'S','a','t','u','r','d','a','y','\0'},
		   {'S','u','n','d','a','y','\0'}};
  start = getdays(4,12);//初始日期
  startweekday = 4;//初始星期
  while(1)
    {
      printf("请输入终止月:");
      scanf("%d", &endmonth);
      printf("请输入终止日:");
      scanf("%d", &endday);
      end = getdays(endmonth, endday);
      if(end < start)
	{
	  printf("终止日期要大于4月12日！请重新输入...\n");
	}
      else
	{
	  dayspan = end - start;
	  weekday = dayspan%7;
	  result = (startweekday+weekday-1)%7;
	  puts(week[result]);
	  break;
	}
    }
  return 1;
}