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String concatenation

Learn string concatenation with + and fmt.Sprintf.

String concatenation

There are three common ways to join a few pieces:

ad, soyad := "Ada", "Lovelace"
tam := ad + " " + soyad                    // 1) the + operator
tam = fmt.Sprintf("%s %s", ad, soyad)       // 2) Sprintf
tam = strings.Join([]string{ad, soyad}, " ") // 3) Join

For a few pieces +, when formatting is needed Sprintf, and when joining a slice with a separator Join is the most readable.

strings.Builder

strings.Builder adds text piece by piece and produces a single string at the end:

var b strings.Builder
for i := 1; i <= 3; i++ {
    if i > 1 {
        b.WriteString(", ")
    }
    fmt.Fprintf(&b, "madde %d", i)
}
fmt.Println(b.String())  // madde 1, madde 2, madde 3

Because Builder is an io.Writer, fmt.Fprintf can write to it directly; if the size is known, reserve room with b.Grow(n).

Practice List text

Join the slice meyveler := []string{"elma", "armut", "kiraz"} with strings.Join using the separator ", " and print it with fmt.Sprintf("%d meyve: %s", ...).

Starter code

main.go
package main

import (
    "fmt"
    "strings"
)

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import (
    "fmt"
    "strings"
)

func main() {
    meyveler := []string{"elma", "armut", "kiraz"}
    fmt.Println(fmt.Sprintf("%d meyve: %s", len(meyveler), strings.Join(meyveler, ", ")))
}

Expected output

3 meyve: elma, armut, kiraz

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What is the most efficient way to join thousands of pieces in a loop?

  • Appending to a []rune
  • strings.Builder Correct answer
  • s += parca
  • fmt.Sprintf at every step

Explanation: Builder collects bytes in a growing buffer; += allocates and copies a new string at every step.

2 Join with a separator

Question 
liste := strings.____([]string{"elma", "armut"}, ", ")
Answer 
liste := strings.Join([]string{"elma", "armut"}, ", ")

Explanation: strings.Join joins slice elements with the given separator.

3 Method and use

Term Meaning
a + b A few pieces
fmt.Sprintf Formatted text
strings.Join Slice + separator
strings.Builder Many pieces in a loop

All lessons in Beginner

1 Go basics

  1. What is Go?
  2. Installing Go
  3. Your first program
  4. go run and go build
  5. Comments and semicolons
  6. Summary - Go basics

2 Modules

  1. go mod init
  2. package and import
  3. The main package
  4. Multiple files
  5. go.sum and dependencies
  6. Summary - Modules

3 Variables

  1. Declaration with var
  2. Short declaration :=
  3. const and iota
  4. Zero value
  5. Type inference
  6. Summary - Variables

4 Data types

  1. int and float
  2. bool and string
  3. byte and rune
  4. Type conversion
  5. Type definitions
  6. Summary - Data types

5 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Command-line menu

6 Functions

  1. func declaration
  2. Parameters and return
  3. Multiple return
  4. Variadic functions
  5. Anonymous functions
  6. Summary - Functions

7 Control flow

  1. if, else if, else
  2. for loop
  3. Iterating with range
  4. switch and fallthrough
  5. break and continue
  6. Summary - Control flow

8 Array and slice

  1. Array declaration
  2. Slice declaration
  3. Appending with append
  4. Sub-slice
  5. len and cap
  6. Summary - Array and slice

9 Project: Shopping cart

  1. Product struct
  2. Adding to cart
  3. Computing total
  4. Printing the cart

10 Map

  1. Map declaration
  2. Adding elements
  3. Looking up in a map
  4. Deleting from a map
  5. Iterating a map with range
  6. Summary - Map

11 String

  1. String and byte
  2. String concatenation
  3. Conversion with strconv
  4. The strings package
  5. Rune and UTF-8
  6. Summary - String

12 Pointer

  1. What is a pointer?
  2. & and * operators
  3. The new function
  4. Pointers and functions
  5. Nil pointer
  6. Summary - Pointer

13 Struct

  1. Struct declaration
  2. Creating a struct
  3. Field access
  4. Struct embedding
  5. Struct and pointer
  6. Summary - Struct

14 Methods

  1. Method declaration
  2. Pointer receiver
  3. Value receiver
  4. Methods and embedding
  5. Method chaining
  6. Summary - Methods

15 Interface and error

  1. Interface declaration
  2. Implicit satisfaction
  3. The error interface
  4. Returning errors
  5. errors.Is and errors.As
  6. Summary - Interface and error

16 Beginner final

  1. Challenge 1 - Combined program
  2. Challenge 2 - Data structure
  3. Challenge 3 - Error handling
  4. Challenge 4 - Mini app