4.1.到100的累加

package study;

public class Main {
	public static int sum=0;	
	public static int add(int n) {
		if(n!=0) {
			sum+=n;
			add(--n);
		}			
		return sum;
	}
	
	public static void main(String[] args) {
		System.out.println(add(100));
	}

}