Golang GUI Calculator

#go #beginners #tutorial #programming

In this article you will learn, how you can build a calculator from scratch. We’ll focus on the Go and it’s Fyne package which helps to create GUI based application for every operating system even for mobile so if you want to learn more about Fyne or if you are new to Go then you need to cover Go and Fyne first.

Packages used

The packages we are going to use in this program are mentioned below:

Fyne for creating GUI and it’s all Components.
GoValuate provides support for evaluating arbitrary C-like artithmetic/string expressions so we can get the result of used expression.

Fyne Package

Fyne is an easy-to-use UI toolkit and app API written in Go. It is designed to build applications that run on desktop and mobile devices with a single codebase.

To develop apps using Fyne you will need Go version 1.14 or later, a C compiler and your system’s development tools. If you’re not sure if that’s all installed or you don’t know how then check out Getting Started document.

Code

package main

import (
    "strconv"

    "fyne.io/fyne/v2/app"
    "fyne.io/fyne/v2/container"
    "fyne.io/fyne/v2/widget"
    "github.com/Knetic/govaluate"
)

func main() {
    myApp := app.New()
    myWindow := myApp.NewWindow("Calculator")

    mainResult := widget.NewLabel("")

    mainS := ""
    mainResult.SetText(mainS)

    one := widget.NewButton("1", func() {
        mainS += "1"
    })
    two := widget.NewButton("2", func() {
        mainS += "2"
    })
    three := widget.NewButton("3", func() {
        mainS += "3"
    })
    four := widget.NewButton("4", func() {
        mainS += "4"
    })
    five := widget.NewButton("5", func() {
        mainS += "5"
    })
    six := widget.NewButton("6", func() {
        mainS += "6"
    })
    seven := widget.NewButton("7", func() {
        mainS += "7"
    })
    eigth := widget.NewButton("8", func() {
        mainS += "8"
    })
    nine := widget.NewButton("9", func() {
        mainS += "9"
    })
    zero := widget.NewButton("0", func() {
        mainS += "0"
    })

    clear := widget.NewButton("C", func() {
        mainS = ""
    })

    plus := widget.NewButton("+", func() {
        mainS += "+"
    })

    minus := widget.NewButton("-", func() {
        mainS += "-"
    })

    multiply := widget.NewButton("*", func() {
        mainS += "*"
    })

    divide := widget.NewButton("/", func() {
        mainS += "/"
    })

    #fourth
    equal := widget.NewButton("=", func() {
        expression, err := govaluate.NewEvaluableExpression(mainS)
        if err == nil {
            result, err := expression.Evaluate(nil)
            if err == nil {
                mainS = strconv.FormatFloat(result.(float64), 'f', -1, 64)
            } else {
                mainS = err.Error()
            }
        } else {
            mainS = err.Error()
        }
    })

    #five updating it each time
    go func() {
        for {
            mainResult.SetText(mainS)
        }
    }()

    #creating layout from the given buttons
    myWindow.SetContent(container.NewVBox(
        mainResult,
        container.NewGridWithColumns(3,
            divide,
            multiply,
            minus,
            // plus,
        ),
        container.NewGridWithColumns(2,
            container.NewGridWithRows(3,
                container.NewGridWithColumns(3,
                    seven,
                    eigth,
                    nine,
                ),
                container.NewGridWithColumns(3,
                    four,
                    five,
                    six,
                ),
                container.NewGridWithColumns(3,
                    one,
                    two,
                    three,
                ),
            ),
            plus,
        ),
        container.NewGridWithColumns(2,
            container.NewGridWithColumns(2,
                clear,
                zero,
            ),
            equal,
        ),
    ),
    )
    myWindow.ShowAndRun()
}