004.c

// 【程序4】
// 题目：输入某年某月某日，判断这一天是这一年的第几天？
// 1.程序分析：以3月5日为例，应该先把前两个月的加起来，然后再加上5天即本年的第几天，特殊情况，四年一次的闰年且输入月份大于3时需考虑多加一天。
// 2.程序源代码：
main() {
  int day, month, year, sum, leap;
  printf("\nplease input year,month,day\n");
  scanf("%d,%d,%d", &year, &month, &day);
  switch (month) { /*先计算某月以前月份的总天数*/
  case 1: sum = 0; break;
  case 2: sum = 31; break;
  case 3: sum = 59; break;
  case 4: sum = 90; break;
  case 5: sum = 120; break;
  case 6: sum = 151; break;
  case 7: sum = 181; break;
  case 8: sum = 212; break;
  case 9: sum = 243; break;
  case 10: sum = 273; break;
  case 11: sum = 304; break;
  case 12: sum = 334; break;
  default: printf("data error"); break;
  }
  sum = sum + day; /*再加上某天的天数*/
  if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) /*判断是不是闰年*/
    leap = 1;
  else
    leap = 0;
  if (leap == 1 && month > 2) /*如果是闰年且月份大于2,总天数应该加一天*/
    sum++;
  printf("It is the %dth day.", sum);
}