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miniscript-rag-corpus

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![](chinchilla-01.svg)
{chapterHead: "Day 6: If and Break", startingPageNum:53}
{width: "50%"}
![](Chapter6.svg)
Q> In the end, there can be only one `else` block.
Q> Or none. That's cool too.
Q>— The Highlander
A> **Chapter Objectives**
A> - Learn how a computer program can do different things depending on what values it currently has.
A> - Explore the various forms of the `if` statement.
A> - Learn how to short-cut or exit a loop.
In the last chapter, we learned how to compare values, and applied that new power to the `while` loop. But, it turns out, that's a little bit like learning to cook and then only doing so for breakfast. It's a perfectly valid use of your skill, but misses the most common application. In programming, comparing values ...
{i:"`if`"}
An `if` statement does just what it sounds like: it tells the computer to do something only *if* some condition is true. Let's look at a simple example:
{caption:Our first `if` statement}
```miniscript
age = val(input("Enter your age: "))
if age > 23 then
print "Wow, you're old!"
end if
print "OK, got it."
```
Line 1 of this example should be familiar to you; it displays a prompt, waits for the user to type something and press Return, converts this to a number using `val`, and stores it in a variable called `age`.
The new bit is on line 2. It says that *if* (and *only* if!) age is greater than 23, *then* the computer should actually do line 3. If not, then the computer should just skip on down to the `end if` line.
Note how, just as with `while` and `for` loops, we indent the body of the `if` block (everything between `if` and `end if`) for clarity. But again, that indentation is like a comment; it's for the human readers of the code, and ignored by the computer. But that doesn't mean you shouldn't do it!
Also notice that there are two new keywords on line 2: `if` and `then`. An `if` statement always has both of these keywords, working together. The actual condition lies in between.
Type in the above code and run it several times, testing it with different ages. (It's totally OK to lie about your age when testing a program.)
## Doing Something Else
The above example prints an extra message when an age over 23 is entered. You may have wondered how to print a different extra message for younger users. You could do it with another `if` block, like so:
{caption:Life without `else`}
```miniscript
age = val(input("Enter your age: "))
if age > 23 then
print "Wow, you're old!"
end if
if age <= 23 then
print "Not so old, are you?"
end if
print "OK, got it."
```
That works, but it's a pain; we have to think about what the opposite of the original comparison is (changing `> 23` to `<= 23` in this case). Worse, if we ever change the initial `if` statement, we'll have to remember to change the second one accordingly. That's just inviting mistakes. Programming is all about maki...
Fortunately, there's a much better way to express what we're trying to do here, and that is the `else` statement. The word `else`, on a line all by itself, identifies code that the computer should run when the condition in the `if` statement is *not* true.
{caption:`else` to the rescue}
```miniscript
age = val(input("Enter your age: "))
if age > 23 then
print "Wow, you're old!"
else
print "Not so old, are you?"
end if
print "OK, got it."
```
This is much better! Now when the computer gets to line 2, it's going to check the age, and then print one message or the other, but never both.
## Checking Multiple Possibilities
Sometimes there are multiple possibilities you want to check for, and run code corresponding only to the one that is true. You can do this using `else if` blocks.
Extending the previous example, suppose we want the computer to comment on several different age ranges.
{caption:Being snarky to all ages}
```miniscript
age = val(input("Enter your age: "))
if age > 60 then
print "Distinguished indeed."
else if age > 23 then
print "Older than dirt! (Dirt's 23.)"
else if age > 17 then
print "Be sure to vote!"
else if age > 12 then
print "Ah, the teenage years."
else if age < 1 then
print "I don't think that's right."
else
print "Just a young'un!"
end if
print "Seriously though, thanks for telling me."
```
In this example there are actually four `else if` blocks, but you can have any number of these (including none at all). Here's how it works: the computer first checks the condition on the `if` statement. If that's true, then it runs the code in that very first block (line 3 in the example above), and then jumps on do...
To review, a complete `if` statement consists of: