# Variables and Constants

> Declaration and initialization of variables/constants

\ <br>

## Before getting started

<br>

### Constants

* Variables that cannot change their values
  * **const** in Javascript!

#### Untype constant

* Constants without type
  * ex)

    ```go
    package main

    func main() {
     const name = "chloe"
    }
    ```

#### Type constant

* Constants with type
  * ex)

    ```go
    package main

    func main() {
      const name string = "chloe"
    }
    ```
* Of course, since it's a constant, you cannot change the value!
  * ex)

    ```go
    package main

    func main() {
      const name string = "chloe"
      name = "camila" // -> not possible
    }
    ```

<br>

### Variables

* Literally variables (values can be changed)
  * **let** in Javascript!

#### Untype variable

* Variables without type
  * ex)

    ```go
    package main

    import "fmt"

    func main() {

     var year = 2020
     fmt.Println(year)

    }
    ```

#### Type variable

* Variables with type
  * ex)

    ```go
    package main

    import "fmt"

    func main() {

     var month int = 12
     // -> month := 12 (same)

     fmt.Println(month)
    }
    ```

<br>

### Types in Go

* Go tries to figure out the type of the value you wrote
  * Because Go is a **type language**!
    * Must tell what the *"Type is!"*
      * Like Java or typescript, you need to specify the type

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## 1. Declaring variables

<br>

### 1-1. Variable declaration method in Go

#### `var variable_name variable_type`

* You can set initial values right where you declare the variable

  ex)

  ```go
  package main

  func main() {
    var num1 int = 1000
    var num2 int = 1413

    println("Let's do addition ~ ", num1 + num2)
  }
  ```

<br>

### 1-2. `:=`

* Called Short Assignment Statement
* Variable declaration possible **without type declaration**
  * Go finds the type for you!
    * Using this shorthand seems like it can be used flexibly like python!
* Can **only be used inside functions**!!

  ex)

  ```go
  package main

  func main() {
   var a int = 100
   var b string = "Haha"
   c := 200
   print(b, a+c);
  }
  ```

<br>

\
`+`

Be careful that Go generates an error if you create a variable and **don't use it**!