C语言之输入年月日 判断这一天为全年的第几天

#include <stdio.h>
void main()
{
	int year,month,day;
	bool a;
	printf("enter year\n");
	scanf("%d",&year);
	printf("enter month\n");
	scanf("%d",&month);
	printf("enter day\n");
	scanf("%d",&day);
     if((year%4==0&&year%100!=0)||(year%400==0))	
  
	{
		printf("year is run nian \n");
		switch(month)
		{
		case 1 :printf("today is %d",day);
		case 2 :
		        day=+31;
		    	printf("today is %d",day);
				break;
				
		case 3:
			  
			      day=31+28+day;
			
			      printf("today is %d",day);
				  break;
		case 4: day=30+28+30+day;
		     	printf("today is %d",day);
				break;
		case 5: day=88+31+day;
			printf("today is %d",day);
				break;
		case 6:day=88+31+30+day;
				printf("today is %d",day);
				break;
		case 7:day=88+31+30+day+31;
				printf("today is %d",day);
				break;

					case 8:day=88+31+30+day+31+31;
				printf("today is %d",day);
				break;

					case 9:day=88+31+30+day+31+30+30;
				printf("today is %d",day);
				break;
	case 10:day=88+31+30+day+31+30+30+31;
				printf("today is %d",day);
				break;
					case 11:day=88+31+30+day+31+30+30+30+30;
				printf("today is %d",day);
				break;
					case 12:day=88+31+30+day+31+30+30+31+31;
				printf("today is %d",day);
				break;

			   
		
	 }}
}