# Converting & Rounding

[Strongly typed languages](https://en.wikipedia.org/wiki/Strong_and_weak_typing) require the programmer to select a variable type for numbers. For example, an `integer` is a whole number only such as -7 and 30. A `double` or `float` contains values after the decimal like 6.5 or -3.14.\
\
Javascript, on the other hand, treats any variable as a value or string interchangeably, including decimal values. It is a *weakly* or *dynamically* typed language.

### Converting \[String -> Num]

Let's say you are requesting input from the user. They are to type in a number representing the grade they are in and you will be adding 5 to guess their age. You prompt the user, add 5, and output the results... It would go a little like this:

```javascript
let grade = prompt("Please enter your current grade");
let output = grade + 5;
console.log(output);
```

The only problem is that the grade being entered by the user is coming back as a `String` and the `+` operator on strings means to concatenate them. Check it out:

{% embed url="<https://repl.it/repls/MediumorchidGruesomeAdware>" %}

To avoid this, we need to make sure our `grade` variable is being treated as a number. As always, there is more than one way to do this.

#### Number

The Number object in Javascript has many useful functions, not the least of which is returning a new Number if we pass it a string.\
`grade = Number(grade);    // Returns a numeric value of grade, if possible`

#### parseInt or parseFloat

Javascript also has two methods to parse (or convert) a string into a whole number value, `parseInt(string)`, or a decimal value, `parseFloat(string)`.\
`grade = parseInt(grade);    // Returns an integer representation of grade`

It should be noted that the preferred method is to use the `Number` object as it has better handling of non-numeric input.

### Converting \[Num -> String]

Going the other direction is decidedly simpler. Almost anything in Javascript has a `toString()` method which returns a string representation of that variable / object.

```javascript
let num = 15;
let fifteen = num.toString();
console.log(typeof num);     // number
console.log(typeof fifteen); // string
```