# Conditional - If Statement


## If Statements

  * `bool`
    - `true`
    - `false`
  * the _not_ operator
    - `!`
  * initialization statement
  * `if`/`else`
  * `if`/`else`
  * `if`/`else`
  * `if`/`else if`/.../`else`

_If statements_ are conditional statements. Remember in control flow, we have sequence, we have iterative, and we also have conditional. Sequence is top to bottom, iterative is looping, and conditional is based upon a condition it will either do one thing or another.

Let's start with some predeclared constants, `true` and `false` and not true `!true` and not false `!false`

```go
package main

import (
	"fmt"
)

func main() {
	if true {
		fmt.Println("001")
	}

	if false {
		fmt.Println("002")
	}

	if !true {
		fmt.Println("003")
	}

	if !false {
		fmt.Println("004")
	}
}
```

[playground](https://play.golang.org/p/Aok8L_OVMo)

Following through the example above, we see `if true` which will always be true, and will execute. `if false` will always be false, and will not execute. `if !true` is if _not_ true, which is the same as false, and will _not_ execute, while `if !false` is if _not_ false, which will execute.

Let's try with some more examples using numbers and the not operator `!`:

```go
package main

import (
	"fmt"
)

func main() {
	if 2 == 2 {
		fmt.Println("001")
	}

	if 2 != 2 {
		fmt.Println("002")
	}

	if !(2 == 2) {
		fmt.Println("003")
	}

	if !(2 != 2) {
		fmt.Println("004")
	}
}
```

[playground](https://play.golang.org/p/Q1QjvxZzFX)

In Go, we mostly don't see [semicolons](https://golang.org/doc/effective_go.html#semicolons) at the end of statements in source. Though we do see them in initialization statments.

So, if we want to have two statements on one line, we can use a semicolon.

```go
package main

import (
	"fmt"
)

func main() {
	fmt.Println("here's a statement"); fmt.Println("something else")
}
```

If you run format, the formatter will put this over two lines.

One usecase would be initialization of a variable and evaluation, for example `if x := 42; x == 2` will initialize the variable `x` with the value of `42` then will evaluation the expression `x == 2` which is `false`

```go
package main

import (
	"fmt"
)

func main() {
	if x := 42; x == 2 {
		fmt.Println("001")
	}
	fmt.Println("here's a statement")
	fmt.Println("something else")
}
```

[playground](https://play.golang.org/p/araiTmOGMJ)