Go Variables
A variable is a named place that stores a value. A program can read the value and change it later.
Declare, assign, and print
The word string is the type. A type says what kind of value a variable holds.
package main
import "fmt"
func main() {
var name string
name = "Hana"
fmt.Println(name)
}A short declaration
The := form declares and sets a value at once. Go reads the type from the value.
package main
import "fmt"
func main() {
city := "Seattle"
fmt.Println(city)
}Two variables on one line
One var line declares both variables. A later line changes only the second value.
package main
import "fmt"
func main() {
var first, second int = 3, 4
second = 10
fmt.Println(first, second)
}Zero values
No line sets a value for these variables. Printf shows the zero value of each type.
package main
import "fmt"
func main() {
var count int
var name string
var ready bool
fmt.Printf("[%d][%s][%t]", count, name, ready)
}A variable must be used
This program declares a variable and never uses it. The compiler refuses the program.
package main
import "fmt"
func main() {
score := 90
fmt.Println("Game over")
}Example
package main
import "fmt"
func main() {
name := "Hana"
level := 3
fmt.Println("Name:", name)
fmt.Println("Level:", level)
}Key points
- Use var to declare a variable.
- A var line names a type for the variable.
- Assign a value with the = sign.
- Use := to declare a variable and set its value in one line.
- Go reads the type from the value in a := line.
- One line can declare two variables of the same type.
- A variable with no set value holds the zero value of its type.
In this example, the first line sets name to Hana with a short declaration. The second line sets level to 3. The two print lines show each value beside its label.
Note
Every declared variable must be used in the program.
Try it Yourself
Edit the code, then press Run.
Running is simulated · Go Playground
Exercise
Which line declares a variable and sets its value at once?