# 11. Constants

### What are constants?

A `const` declaration defines named values that look syntactically like variables but whose value is constant.Instead of the `var` keyword, we use the `const` keyword.A value must be assigned while declaring constants.Constants only exists during compile time!

### Declaring constants

Constants are declared using `const` keyword.

{% code title="main.go" %}

```go
const pi = 3.14
```

{% endcode %}

### Constant Block

Similar to variable block, we can also have constant block.

{% code title="main.go" %}

```go
const (
	pi         = 3.14
	daysInWeek = 7
)
```

{% endcode %}

### IOTA

`iota` can be used to create enumerated constants. It is also called as constant generator.

{% code title="main.go" %}

```go

const (
	Sunday int = iota
)

func main() {
	fmt.Println(Sunday)
}
```

{% endcode %}

Benefits of using iota is that it will increment itself for next const declaration in same const block.

{% code title="main.go" %}

```go

const (
	Monday int = iota + 1
	Tuesday
	Wednesday
	Thursday
	Friday
	Saturday
	Sunday
)

func main() {
	fmt.Println(Monday, Tuesday, Wednesday, Thursday, 
	Friday, Saturday, Sunday)
}
// output : 1 2 3 4 5 6 7
```

{% endcode %}

### From the Docs

{% embed url="<https://golang.org/doc/effective_go.html#constants>" %}
Constants
{% endembed %}

### Blog Posts

{% embed url="<https://blog.golang.org/constants>" %}

{% embed url="<https://github.com/golang/go/wiki/Iota>" %}

{% embed url="<https://dlintw.github.io/gobyexample/public/constants-and-iota.html>" %}

{% embed url="<https://splice.com/blog/iota-elegant-constants-golang/>" %}