String Basics
Go strings are immutable sequences of bytes, typically UTF-8 encoded. A string is essentially a read-only []byte with a length. This means indexing a string gives you a byte, not a character.
s := "Hello, World!"
fmt.Println(len(s)) // 13 (bytes, not characters)
fmt.Println(s[0]) // 72 (byte value of 'H')
fmt.Printf("%c\n", s[0]) // H (as character)
// Strings are immutable
// s[0] = 'h' // compile error!Runes — Unicode Characters
A rune is an alias for int32 and represents a Unicode code point. For ASCII, one byte = one rune. But multi-byte characters (emoji, Chinese, etc.) use multiple bytes for one rune.
s := "Hello, 你好!"
fmt.Println(len(s)) // 14 (bytes)
fmt.Println(len([]rune(s))) // 9 (characters/runes)
// range iterates RUNES, not bytes (correct!)
for i, ch := range s {
fmt.Printf("%d: %c (U+%04X)\n", i, ch, ch)
}range to iterate over strings — it correctly handles multi-byte UTF-8 characters. Use len([]rune(s)) for character count, len(s) for byte count.The strings Package
import "strings"
s := " Hello, World! "
fmt.Println(strings.TrimSpace(s)) // "Hello, World!"
fmt.Println(strings.ToUpper("hello")) // "HELLO"
fmt.Println(strings.Contains(s, "World")) // true
fmt.Println(strings.Replace(s, "World", "Go", 1))
fmt.Println(strings.Split("a,b,c", ",")) // [a b c]
fmt.Println(strings.Join([]string{"a","b"}, "-")) // "a-b"
fmt.Println(strings.HasPrefix("golang", "go")) // trueEfficient String Building
// Bad: string concatenation in loop (O(n^2))
// s := ""
// for _, word := range words { s += word + " " }
// Good: strings.Builder (O(n))
var b strings.Builder
for _, word := range []string{"Hello", "from", "Go"} {
b.WriteString(word)
b.WriteByte(' ')
}
fmt.Println(b.String()) // "Hello from Go "⚠️ Common Mistake: String concatenation in loops
Strings are immutable. Each += creates a new string and copies all previous bytes. For n words, this is O(n²). Use strings.Builder or strings.Join() instead.
Practice Exercises
Easy Hello World Variant
Modify the example to accept user input and print a personalized greeting.
Easy Code Reading
Read through the code examples above and predict the output before running them.
Medium Extend the Example
Take one code example and add error handling, input validation, or a new feature.