浅谈选择结构if语句和switch语句的区别

import java.util.Scanner;
class Demo_If {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);  //键盘输入,
    while(true) {
    System.out.println("请您输入成绩");  //提示输入
    int a = sc.nextInt();          //键盘输入用int类型接收
    if (a>100|a<0) {            //死循环,方便测试
      System.out.println("您输入的成绩有误");
    }else if (a>=90&a<=100) {
      System.out.println("A等");
    }else if (a>=80&a<90) {
      System.out.println("B等");
    }else if (a>=70&a<80) {
      System.out.println("C等");
    }else if (a>=60&a<70) {
      System.out.println("D等");
    }else if (a<60) {
      System.out.println("E等");
    }else {
      System.out.println("您输入的成绩有误");
    }
    }
}
}

import java.util.*;
class Dome_If3{
  public static void main(String[] args) {
    //System.out.println("Hello World!");
    Scanner sc =new Scanner(System.in);    //键盘录入
    while(true) {                //死循环方便测试
    System.out.println("请您  输入要转换的星期数"); //键盘录入提示
    in week = sc.nextInt();
    switch(week) {
      case 1:
        System.out.println("星期1");
      break;
      case 2:
        System.out.println("星期2");
      break;
      case 3:
        System.out.println("星期3");
      break;
      case 4:
        System.out.println("星期4");
      break;
      case 5:
        System.out.println("星期5");
      break;
      case 6:
        System.out.println("星期6");
      break;
      case 7:
        System.out.println("星期天");
      break;
      default:
        System.out.println("您输入的数字有误,请重新输入");
    }
   }
  }
}