if、while、do while 、switch

JavaScript的循环

if  while switch do while

if

function fun(){
     var 	num1 =  prompt("请输入一个数！"),
           	num2 =  prompt("请输入一个数！"),
           	sum;
           	if(num1 > num2){
              sum = num1 + num2;
}
            else{
              sum = num2 - num1;
}
}

while与do while的区别：
while是先判断再执行，而do while是先执行再判断。
while

function fun(){
           var sum;
           var a = 10;
           var b = 20;
           while(b>=a){
           sum = b / a;
           }
}

do while

function fun(){
           var sum;
           var a = 10;
           var b = 20;
           do{
           sum = b / a;
           }
           while(b>=a)
}

switch

猜数游戏
function game(){
var num1;
var num = Math.floor((Math.random(10)*10));
while (num != num1 || num == exit) {
num1 = prompt(“请输入一个数！”);
switch (true) {
case num == num1:
alert(“猜对了”);
break;
case num1 > num && num1 != “”:
alert(“猜大了”);
break;
case num1 < num && num1 != “”:
alert(“猜小了”);
break;
case num1 == exit :
alert(“退出游戏！”);
break;
default:
alert(“输入有误”)
break;
}
}
}
game();