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Go Basics

Reading User Input in Go

Read a line with bufio, trim it and convert it to a number without crashing on bad input.

  • Beginner
  • 3 min read
  • 1 runnable example
What you'll learn
  • bufio.NewReader
  • strings.TrimSpace
  • strconv.Atoi
Run code →
From the keyboard to a number
  1. 1ReadString"36\n"
  2. 2TrimSpace"36"
  3. 3strconv.Atoi36, nil
  4. 4age + 137

Text in, number out

bufio.NewReader reads from the keyboard one line at a time. The text always arrives as a string, so numbers must be converted with strconv before you calculate with them.

ReadString('\n') returns everything up to the Enter key, and TrimSpace removes the line ending. strconv.Atoi returns the number and an error; the error is not nil when the text is not a number. The sample output uses the answers Ada and 36: in the online compiler, type your answers when the prompts appear.

Key points

  1. ReadString('\n') reads up to the Enter key.
  2. TrimSpace removes the line ending.
  3. Atoi returns the number and an error.

Runnable Go example

Go
Run code →
main.go
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	reader := bufio.NewReader(os.Stdin)

	fmt.Println("What is your name?")
	name, _ := reader.ReadString('\n')
	name = strings.TrimSpace(name)

	fmt.Println("How old are you?")
	text, _ := reader.ReadString('\n')

	age, err := strconv.Atoi(strings.TrimSpace(text))
	if err != nil {
		fmt.Printf("Hello, %s! That is not a number.\n", name)
		return
	}
	fmt.Printf("Hello, %s! Next year you will be %d.\n", name, age+1)
}
Get a Run button for this example Result of running the code
What is your name?
How old are you?
Hello, Ada! Next year you will be 37.

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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Next: Conditions: if and switch →

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