期末复习

package 练习;
import java.util.Scanner;
public class 计算 {
    public static void main(String[] args) {
           int sum=0;
           System.out.println("请选择需进行的操作：");
           Scanner rd = new Scanner(System.in);
           int num;
            num=rd.nextInt();
            switch(num){
            case 1:
             for(int i=0;i<=100;i++) {
                  sum=i+sum;
                  }
             System.out.println("自然数之和为："+sum);
             break;
            case 2:
                for(int i=0;i<=100;i++) {
                      if(i%2==1)
                    sum=i+sum;
                      }
                 System.out.println("奇数之和为："+sum);
                break;
            case 3:
                for(int i=0;i<=100;i++) {
                      if(i%2==0)
                    sum=i+sum;
                      }
                 System.out.println("偶数之和为："+sum);
                break;
        }
    }
    }