Go — Strings

String basics

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "Hello, World!"
    raw := `Raw string
with newlines`

    fmt.Println(s)
    fmt.Println(raw)
    fmt.Println(len(s))         // 13
    fmt.Println(s[0])           // 72 (byte value)
    fmt.Println(string(s[0]))   // H
}

String operations

s := "Hello, World!"

fmt.Println(len(s))                          // 13
fmt.Println(strings.ToUpper(s))              // HELLO, WORLD!
fmt.Println(strings.ToLower(s))              // hello, world!
fmt.Println(strings.Contains(s, "World"))    // true
fmt.Println(strings.HasPrefix(s, "Hello"))   // true
fmt.Println(strings.HasSuffix(s, "!"))       // true
fmt.Println(strings.Index(s, "World"))       // 7
fmt.Println(strings.Replace(s, "World", "Go", 1)) // Hello, Go!
fmt.Println(strings.Repeat("ab", 3))         // ababab

Split and join

csv := "apple,banana,cherry"

// Split
fruits := strings.Split(csv, ",")
fmt.Println(fruits) // [apple banana cherry]

// Join
joined := strings.Join(fruits, " | ")
fmt.Println(joined) // apple | banana | cherry

String formatting

name := "Alice"
age := 30

// fmt.Sprintf
s := fmt.Sprintf("Name: %s, Age: %d", name, age)
fmt.Println(s)

// Format specifiers
fmt.Printf("%q\n", "hello")       // "hello"
fmt.Printf("%-10s\n", "left")     // "left      "
fmt.Printf("%10s\n", "right")     // "     right"
fmt.Printf("%05d\n", 42)          // 00042
fmt.Printf("%.2f\n", 3.14159)     // 3.14

Bytes and runes

s := "Hello, 你好!"

// Bytes
bytes := []byte(s)
fmt.Println(bytes)

// Runes (Unicode code points)
runes := []rune(s)
fmt.Println(runes)
fmt.Println(len(runes)) // 9 (not 13)

// Iterate by rune
for i, r := range s {
    fmt.Printf("Index %d: %c\n", i, r)
}

String conversion

import (
    "strconv"
    "fmt"
)

// Number to string
s := strconv.Itoa(42)     // "42"
s = strconv.FormatFloat(3.14, 'f', 2, 64) // "3.14"

// String to number
n, err := strconv.Atoi("42")
f, err := strconv.ParseFloat("3.14", 64)

fmt.Println(s, n, f)

Builder

import "strings"

var builder strings.Builder
for i := 0; i < 1000; i++ {
    builder.WriteString("a")
}
result := builder.String()

Mini Practice

Write Go code that:

1. Splits a CSV string into fields
2. Joins a slice of strings with a delimiter
3. Counts occurrences of a character in a string
4. Uses strings.Builder for efficient string concatenation

Up Next

In the next lesson, you'll learn about If Else — conditional branching in Go.