String and byte
- Go course
- Beginner
- Lesson 57/90
- 4 min
Learn the byte slice behind a string.
Strings and bytes
A Go string is an immutable sequence of bytes. You can't change a character in place; s[0] = 'G' is a compile error. To change it, convert to []byte (or []rune for Turkish letters) and build a new string:
s := "merhaba"
b := []byte(s)
b[0] = 'M'
fmt.Println(string(b)) // Merhabas[i] gives a byte, not a string.
Why immutability helps
Because strings are immutable they can be shared safely, and substrings (s[2:5]) point at the same bytes without copying. The cost: s += "x" in a loop allocates a new string every time. When building text from many pieces, use strings.Builder (you'll see it in the concatenation lesson).
Practice Capitalize the first letter
Declare s := "golang". Convert it to []byte, set the first byte to 'G' and print the new string.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func main() {
s := "golang"
b := []byte(s)
b[0] = 'G'
fmt.Println(string(b))
}Expected output
Golang
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does <code>fmt.Println("Go"[0])</code> print?
- "G"
- An error
- 71 (the byte value of G) Correct answer
- G
Explanation: Indexing returns a byte (uint8); to see it as a letter use string("Go"[0:1]) or %c.
2 Convert to a byte slice
b := []____(s)
b[0] = 'M'b := []byte(s)
b[0] = 'M'Explanation: []byte(s) creates a modifiable byte copy of the string.
3 Expression and type
| Term | Meaning |
|---|---|
"Go" |
string |
"Go"[0] |
byte (71) |
"Go"[0:1] |
string ("G") |
[]byte("Go") |
[71 111] |