Question

有人可以为我解释这个循环吗？它是自由代码阵营中罗马数字挑战的一部分 - 它不是我的，我做了我自己的，但它是更多的代码。我正在努力了解这一点以改善我自己。无论如何，while循环完全抛弃了我。任何帮助都会很棒。

function romans(num){
    var roman = "";
    var romanNumerals = ["M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"];
    var numbers = [1000,900,500,400,100,90,50,40,10,9,5,4,1];

    for (var i=0; i<numbers.length; i++) {
        //If the num was 5 then then it would read 5 greater than 1000?
        while (num >= numbers[i]) {
            roman = roman + romanNumerals[i]
            //5 minus 1000? 
            num = num - numbers[i]
        }
    }

    return roman;
}

console.log(romans(5))

Answer 1

num作为所需的输入开始，然后您会找到加起来为num的数字，从最大的罗马数字（numbers[0]）开始。

您使用while循环重复，因为您可能需要多个字母副本（即"III" == 3）

romans(5)在numbers[10]之前不会触发while循环（因为正如你所说5 >= 1000 == false），此时你将字符V追加到roman，并减去5来自num。由于num现在为0，因此while循环将永远不会再触发。

尝试使用romans(3001)进行思考，你会看到m / 1000的while循环触发3次，然后跳过10次，然后触发I / 1

Answer 2

function romans(num){
var roman = "";
var romanNumerals=["M","CM","D","CD","C","XC","L","XL","X",
"IX","V","IV","I"];
var numbers = [1000,900,500,400,100,90,50,40,10,9,5,4,1];

for (var i=0; i<numbers.length; i++){

    //If the num was 5 then then it would read 5 greater than 1000?
    console.log("comparing: " + numbers[i]);
    console.log(" with: " + num);
    while(num >= numbers[i]){
    console.log("entered");
        roman = roman + romanNumerals[i]
        //5 minus 1000? 
        num = num - numbers[i]
        console.log('subtracting: ' + numbers[i]);
        }
    }
    return roman
}
console.log(romans(44))

它将沿着数字线向下，直到找到一个更小的数字：例如44：

在for for it中它将遍历数字数组，直到它找到一个数字然后是44（在迭代之前永远不会输入while循环）。

当它找到一个小于44的数字时，它进入while循环并在该迭代中取i的位置处的romanNumerals，在这种情况下为40.然后它将原始数字降低40（44-40 = 4）并且然后退出循环返回到for以搜索低于4的数字。

while循环javascript逻辑

2 个答案: