import java.util.Scanner;
public class Thirtheen {
	/*输入某年某月某日,判断这一天是这一年的第几天?*/
	public static void main(String[] args){
		Scanner input=new Scanner(System.in);
		int sum,i;
		System.out.print("请输入年份:");
		int a=input.nextInt();
		System.out.print("\n");
		System.out.print("请输入月份:");
		int b=input.nextInt();
		System.out.print("\n");
		System.out.print("请输入日:");
		int c=input.nextInt();
		System.out.print("\n");
		
		if(a%4==0&&a%100!=0&&b>1)
			sum=29;
		else if(b>1)
			sum=28;
		else
			sum=0;
		for(i=1;i<b;i++){
			if(i==2)
				continue;
			switch(i){
			case 1: case 3: case 5: case 7: case 8: case 10: case 12:
				sum=sum+31;
			case 4: case 6: case 9: case 11: 
				sum=sum+30;
				
			}
		}
		sum=sum+c;
		System.out.println("到"+a+"年"+b+"月"+c+"日"+","+a+"年过去了"+sum+"天");
		
	}
}
原文:http://www.cnblogs.com/yjh123/p/6352224.html