C语言函数练习题

题目：编写函数，计算某月某日是该年度的第几天。

include 
/declare/
 int how_many_days_before_the_day(int month, int day);
 int day_of_year(int month, int day, int year);
int main()
 {
 int n = 0, MONTH, DAY;
 printf("Month: ");
 scanf("%d", &MONTH);
 printf("Day: ");
 scanf("%d", &DAY);
 n = how_many_days_before_the_day(MONTH, DAY);
 printf("DAYS = %d\n", n);
 return 0;
 }
/define/
 int how_many_days_before_the_day(int month_input, int day_input){
 int days_in_month[12];
 int month;
 for (month = 0; month < 12; ++month)
 {
 int month_plus;
 month_plus = month + 1;
 switch(month_plus){
 case 1:
 case 3:
 case 5:
 case 7:
 case 8:
 case 10:
 case 12:
 days_in_month[month] = 31;
 break;
 case 4:
 case 6:
 case 9:
 case 11:
 days_in_month[month] = 30;
 break;
 case 2:
 days_in_month[month] = 28;
 break;
 }
 }
 //every month now has its day-number, month[0-11].
 int total_before_the_month = 0;
 for (month = 0; month < (month_input - 1); ++month)
 {
 printf("Days in month %d = %d\n", month + 1, days_in_month[month]);
 total_before_the_month = total_before_the_month + days_in_month[month];
 }
 int total;
 total = total_before_the_month + day_input;
 return total;
 }