java学习系列3--流程控制语句

Posted 2021-03-18 emking

1. 顺序结构

int a = 18;
if(a < 60){
　　return ‘D‘; 
}else if(a<70){
　　return ‘C‘;
}else if(a<80){
　　return ‘B‘;
}else{
　　return ‘A‘;
}

2. 选择结构

int week = 2;
switch (week){
    case 1:
        System.out.println("Monday"); 
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wendesday");
        break;
    default:
        System.out.println("sorry, i dont know");
}

3. 循环结构

int a = 0;
while (a < 0){
    System.out.println(a);
    a++;
}
System.out.println("-----------");
//while和do-while的区别是do-while会保证循环体至少被执行一次
a=0;
do{
    System.out.println(a);
    a++;
}while (a < 0);

//for循环
for (a = 0; a < 0; a++){
    System.out.println(a);
    a++;
}

4. 跳转

//需求1：生成0-100随机数，直到生成88为止，停止循环
int total = 0;
System.out.println("Begin!");
while (true){
    total ++;
    int i = (int)Math.round(100 * Math.random());
    if (i == 88)
        break;
}
System.out.println("Game over,used " + total + "times.");
System.out.println("------------");
//需求2：输出100~150之间不能被3整除的数
for (int i = 100; i < 150; i++){
    if (i % 3 == 0)
        continue;
    System.out.println(i);
}

5. 多重循环

outer: for (int i = 101; i < 150; i++){
  inner:  for (int j = 2; j < i / 2; j++){
        if (i % j == 0){
            continue inner;
        }
        System.out.println(i + " " + j);
    }