# 章序号/节序号/节/笔记序号
codecademy, Variable
# 概念阐释
# 举例子
# 类比、比较与对比
# 问题
[Kelvin Weather](https://www.codecademy.com/courses/introduction-to-javascript/projects/kelvin-weather-javascript)
Deep in his mountain-side meteorology lab, the mad scientist Kelvin has mastered weather prediction.
Recently, Kelvin began publishing his weather forecasts on his website. However there’s a problem: All of his forecasts describe the temperature in [Kelvin](https://en.wikipedia.org/wiki/Kelvin).
With our knowledge of JavaScript, let’s convert Kelvin to Celsius, then to Fahrenheit.
For example, 283 K converts to 10 °C which converts to 50 °F.
Mark the tasks as complete by checking them off
- [x] 1.
The forecast today is `293` Kelvin. To start, create a variable named `kelvin`, and set it equal to `293`.
The value saved to `kelvin` will stay constant. Choose the variable type with this in mind.
- [x] 2.
Write a comment above that explains this line of code.
- [x] 3.
Celsius is similar to Kelvin — the only difference is that Celsius is `273` degrees less than Kelvin.
Let’s convert Kelvin to Celsius by subtracting `273` from the `kelvin` variable. Store the result in another variable, named `celsius`.
- [x] 4.
Write a comment above that explains this line of code.
- [x] 5.
Use this equation to calculate Fahrenheit, then store the answer in a variable named `fahrenheit`.
_Fahrenheit = Celsius * (9/5) + 32_
In the next step we will round the number saved to `fahrenheit`. Choose the variable type that allows you to change its value.
- [x] 6.
Write a comment above that explains this line of code.
- [x] 7.
When you convert from Celsius to Fahrenheit, you often get a decimal number.
Use the `.floor()` method from the built-in Math object to round down the Fahrenheit temperature. Save the result to the `fahrenheit` variable.
>[!hint]
>- 如果数字为，39.3
>- `.ceil`等于40，趋近于最大整数
>- `.floor` 等于39，趋近于最小整数
>- 变量关键字发挥作用，改变变量,变量的最大特点就是可以变
- [x] 8.
Write a comment above that explains this line of code.
- [x] 9.
Use `console.log` and string interpolation to log the temperature in `fahrenheit` to the console as follows:
```
The temperature is TEMPERATURE degrees Fahrenheit.
```
Use string interpolation to replace `TEMPERATURE` with the value saved to `fahrenheit`.
- [x] 10.
Run your program to see your results!
- [x] 11.
By using variables, your program should work for any Kelvin temperature — just change the value of `kelvin` and run the program again.
What’s `0` Kelvin in Fahrenheit?*-273度*
- [x] 12.
Great work! Kelvin can now publish his forecasts in Celsius and Fahrenheit.
If you’d like extra practice, try this:
- Convert `celsius` to the [Newton](https://en.wikipedia.org/wiki/Newton_scale) scale using the equation below
_Newton = Celsius * (33/100)_
- Round down the Newton temperature using the `.floor()` method
- Use `console.log` and string interpolation to log the temperature in `newton` to the console
# 问题答案
```js
const kelvin = 293; // 设定一个开尔文数
const celsius = kelvin - 273; //摄氏度等于开尔文减去273，这里可以是变量名和数字的组合
let fahrenheit = celsius * (9/5) + 32;//因为下一步需要对数字进行整数处理，所以华氏度的公式用变量关键字
fahrenheit = Math.floor(fahrenheit);//函数总是返回小于等于一个给定数字的最大整数，变量名可以等于一个方法
console.log(`The temperature is ${fahrenheit} degress Fahrenheit.`);
let newton = celsius * (33/100)
newton = Math.floor(newton);
console.log(`The temperature is ${newton}.`)
```
# 备注（经验集/错误集）
[codecademy答案](https://www.codecademy.com/courses/introduction-to-javascript/projects/kelvin-weather-javascript)
- 在数学公式中，变量可以赋值为「另一个变量与数字」的写法，即公式；
- 也可以赋值为一个「方法」（*之前在学方法时都是用在console里*）