const and iota
- Go course
- Beginner
- Lesson 15/90
- 4 min
Learn const for constants and iota for auto-increment.
const and iota
Constant values use the const keyword. After const Pi = 3.14, Pi cannot be changed; it is a compile error.
For enum-like structures, Go uses iota. In a const block, iota increments on each line; the first line starts at 0.
Constants are computed at compile time and do not change at runtime. This makes them preferred for performance and safety.
Using iota
iota produces a line-by-line incrementing number in a const block. For example:
const (
A = iota
B
C
)
Here A=0, B=1, C=2. This is the standard way to define enum-like constants.
iota also works with bitwise ops: 1 << iota yields powers of two on each line.
Practice Days with iota
Define the constants Pazartesi (0), Sali and Carsamba with iota in a const block. Print fmt.Println(Pazartesi, Sali, Carsamba).
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
const (
Pazartesi = iota
Sali
Carsamba
)
func main() {
fmt.Println(Pazartesi, Sali, Carsamba)
}Expected output
0 1 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Can a const value be changed later?
- Yes, with =
- Only inside a function
- No, a compile error Correct answer
- Only through a pointer
Explanation: const values cannot be changed.
2 Constant declaration
To declare the constant Pi:
____ Pi = 3.14To declare the constant Pi:
const Pi = 3.14Explanation: const declares a constant value.
3 Match the constant concepts
| Term | Meaning |
|---|---|
const |
Constant |
iota |
Auto-increment |
Pi = 3.14 |
Fixed value |
const block |
Enum-like |