# If...Else

If you're cold, put on a sweater. If you're hot, take the sweater off. Simple, right?

In code, we need to make several thousand decisions per second. Think of a video game that checks for physical collisions or what happens when you click a certain key on the keyboard. The control of data, or *flow control*, can be determined based on boolean logic. `if` a particular value is true, do something. Otherwise, or `else`, do something else (or nothing at all).

## Syntax

{% tabs %}
{% tab title="C++, Java, and Javascript" %}
Same syntax for C++ , Java, Javascript, and many other languages.

```cpp
if (booleanExpression1) {
   // code to be executed if true
}
else if(booleanExpression2) {
   // booleanExpression1 is false and booleanExpression2 is true
}
else if (booleanExpression3) {
   // booleanExpression1 and 2 are false and booleanExpression3 is true
}
.    // "else if" statements are optional and you can have infinitely many
.
else {
   // code to execute if all test expressions are false (optional)
}
```

{% endtab %}

{% tab title="Python" %}
Python syntax is a bit ~~strange~~ different - there are shortened words, it uses white space to exit a block of code, and notice the placement of colons:

```python
if booleanExpression1:
   # statement(s)
elif booleanExpression2:
   # statement(s)
elif booleanExpression3:
   # statement(s)
else:
   # statement(s)
   
#  Note: "elif" and "else" statements are optional
```

{% endtab %}

{% tab title="Other" %}
`If...else` statements are the most basic tool for creating multiple pathways of code. There can also be shortcuts if you are comparing a simple boolean or want to combine items with `And` or `Or` boolean logic.

There is something called the [**`ternary`**](https://en.wikipedia.org/wiki/%3F:) operator. It is used for simple yes/no situations and is worth learning.

```cpp
// C++ ternary example
int a, b = 2, c = 3;
a = (b > c ? b : c);   // since b > c is false, a takes the value of c (3)
```

{% endtab %}
{% endtabs %}

## Example 1: If

Only do something if the condition is true.

```javascript
let someNumber = 5;

if (someNumber < 0) {
    console.log("That's a negative number");
}

// The above code will do absolutely nothing because 5 is NOT less than 0
```

## Example 2: If...else

Run [the following code](https://replit.com/@MatthewBrash/If-Else-Example) to see how we can do something `else` if the condition is false:

{% embed url="<https://replit.com/@MatthewBrash/If-Else-Example?lite=true>" %}
Example 2: If...else
{% endembed %}

## Example 3: If...else if

We can make a secondary check on a condition if the first condition equates to false. In this example, our third statement equates to `true`, so it is run. Notice how there is no *default* set of code in case none of the conditions equate to true:

```javascript
let myName = "Karen";

if (myName == "Lola") {
    console.log("Her name was Lola...");
}
else if (myName == "Jackie") {
    console.log("You mean, like Jackie Chan? Awesome.");
}
else if (myName == "Karen") {
    console.log("What a lovely name!");
}
else if (myName == "Robert") {
    console.log("His name was Robert Paulson...");
}

// This will output: What a lovely name!
```

## Example 4: If...else if...else

Run [this second example](https://repl.it/repls/ShowyStylishOpenlook) to see multiple options and consider how this sort of conditional code can be used.

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

## Example 5: With Numbers

Finally, just to get the message home, let's [control things based on a number](https://tech.io/snippet/fRXFS4q) instead of text.

{% embed url="<https://tech.io/snippet/fRXFS4q>" %}
Testing Tech.io instead of Repl.it Tech.io is based on Node.js, so no prompt() or alert()
{% endembed %}

## Important Notes

While all of the examples above do a simple `console.log()` it is important to note that you can do whatever you like inside the code block brackets `{ }`. You can even *nest* another `if` statement, loop, function call, or more.

While I would love to continue with more examples, [**they are very easy to find online**](http://lmgtfy.com/?q=javascript+example+if+statement).


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