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An if statement is a control
structure that causes a block of

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code to run under certain conditions.

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It consists of a condition
followed by a block of code and

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the code in the block is run
only if the condition is true.

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So here we have an if statement and

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the condition is the literal boolean value
trick, which of course evaluates the true.

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So the code here in the block
does get executed and

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it prints out the string true.

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You can see that down here in the output.

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Here's another if statement, where
the condition is a simple boolean value,

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it's the value false.

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And, of course, false is not true, so
the code in the block does not run.

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You don't see false down
here in the program output.

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Here's an if statement with
an actual comparison operation.

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The result of is 1 less than 2 is true,
therefore the code in the block runs and

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it prints out the string,
1 is less than 2.

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You can see that here in the output.

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And here's another comparison,
is 1 greater than 2?

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Well, the result of that value is
false and so the block does not run.

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The go language has many of the same
boolean operators that other languages do.

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For example, there's the not operator,
the exclamation point,

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which takes whatever boolean
value it's given and negates it.

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So if it receives the value true,
it will turn it into false.

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So, this if statement, the result is false
and therefore, this code won't be run.

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But this one takes the value false and
makes it true.

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With the result of true
the code in the block does run,

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and you see that it prints
not false down here.

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The operator looks to ensure that
the value on both sides of it is true.

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So, here we have a value that's true on
the left but a false value on the right,

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therefore this entire expression is
false because both values are not true.

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However, down here, we have true on
the left as well as true on the right

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therefore true double and true the result
is true, and this code gets run.

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You can see it on the output.

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The operator with the two vertical bars
here is read as or, it will return

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a true value if either the value on its
left or the value on its right is true.

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So, since this first value
here on the left is true,

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there's no need to even evaluate
the value on the right.

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The results of this expression is true.

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And it prints this line
down here in the output.

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The case is the same here.

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The value on the left is true and
the value on the right is true, but

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that doesn't matter.

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If either one of those had been true,
the result would've been true, and

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the code here in the if
block would have run.

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And again, you can see it in the output.

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The else block goes after an if block, and
it runs only if the if block doesn't run.

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So here we have an if block,
and its condition is true.

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So it does run.

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It prints the expression
if down here in the output.

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But what if we changed this to false so
that it doesn't run?

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Let's try saving that, run this.

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Now that we've changed this to
false the if block doesn't run so

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the else block does.

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And you see else printed
out here on the output.

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You can also use if else blocks.

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So in this code, the condition in
the if statement is true, and so

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the format print line
if statement gets run.

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But if we were to change that to false,
and re-run it,

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then the if statement doesn't get run.

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So it checks the if-else clause,
which it sees is true.

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And because that's true, it will go ahead
and run this block, printing else-if.

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If we were to change
that to false as well.

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Save that, re-run it.

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Now the if clause is false.

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The else if clause is also false.

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And, therefore,
it runs the else clause and prints else.

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Now as before, this code within the curly
braces following the condition of an if

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statement is a block.

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And that means all the same rules
regarding the scope for variables applies.

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So down here where we access
the beforeIf variable,

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that's fine because the beforeIf variable
gets declared before the if block here,

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and therefore it's still
within scope afterwards.

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But here where we try to
print within the if variable,

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that's not okay because it gets defined
within the block for the if statement.

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And, therefore,
it's out of scope down here.

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So, if we try to run this,
we'll see a compile error,

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undefined within if, here on line 12.