main.go

package main

import (
	"strconv"

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



 
func main() {
	a := app.New()
	w := a.NewWindow("Calculator")
	w.Resize(fyne.NewSize(500,280))
	output:=""
	input := widget.NewLabel("")

	historyBtn:= widget.NewButton("History", func() {})

backBtn:= widget.NewButton("Back", func(){
	if len(output)>0{
	output= output[:len(output) - 1];
	input.SetText(output)}
})

clearBtn:= widget.NewButton("Clear", func() {
	output="";
	input.SetText(output);
})

leftBracketBtn:= widget.NewButton("(", func() {
	output=output+"("
	input.SetText(output)
})

rightBracketBtn:= widget.NewButton(")", func() {
	output=output+")"
	input.SetText(output)
})

divideBtn:= widget.NewButton("/", func() {
	output=output+"/"
	input.SetText(output)
})

sevenBtn:= widget.NewButton("7", func() {
	output=output+"7"
	input.SetText(output)
})

eightBtn:= widget.NewButton("8", func() {
	output=output+"8"
	input.SetText(output)
})

nineBtn:= widget.NewButton("9", func() {
	output=output+"9"
	input.SetText(output)
})

starBtn:= widget.NewButton("*", func() {
	output=output+"*"
	input.SetText(output)
})

fourBtn:= widget.NewButton("4", func() {
	output=output+"4"
	input.SetText(output)
})

fiveBtn:= widget.NewButton("5", func() {
	output=output+"5"
	input.SetText(output)
})

sixBtn:= widget.NewButton("6", func() {
	output=output+"6"
	input.SetText(output)
})

minusBtn:= widget.NewButton("-", func() {
	output=output+"-"
	input.SetText(output)
})

oneBtn:= widget.NewButton("1", func() {
	output=output+"1"
	input.SetText(output)
})

twoBtn:= widget.NewButton("2", func() {
	output=output+"2"
	input.SetText(output)
})

threeBtn:= widget.NewButton("3", func() {
	output=output+"3"
	input.SetText(output)
})

plusBtn:= widget.NewButton("+", func() {
	output=output+"+"
	input.SetText(output)
})

zeroBtn:= widget.NewButton("0", func() {
	output=output+"0"
	input.SetText(output)
})

dotBtn:= widget.NewButton(".", func() {
	output=output+"."
	input.SetText(output)
})

equalBtn:= widget.NewButton("=", func() {
	expression, err := govaluate.NewEvaluableExpression(output);
	if err == nil{
		result, err := expression.Evaluate(nil);
		if err == nil{
			output = strconv.FormatFloat(result.(float64), 'f', -1, 64);
		}else{
			output="error";
		}
	}else{
		output="error";
	}

	input.SetText(output)
	
})


	
	w.SetContent(container.NewVBox(
		input,
		container.NewGridWithColumns(1,
		
			container.NewGridWithColumns(2,
			historyBtn,
		backBtn),
		
		container.NewGridWithColumns(4, clearBtn, 
			leftBracketBtn,
		rightBracketBtn,
	divideBtn),

	         container.NewGridWithColumns(4, sevenBtn,
			eightBtn,
		       nineBtn,
	                   starBtn ),

					   container.NewGridWithColumns(4, fourBtn,
					fiveBtn,
				sixBtn,
			minusBtn),

			          container.NewGridWithColumns(4, oneBtn,
					twoBtn,
				threeBtn,
			plusBtn),

					   container.NewGridWithColumns(3, zeroBtn,
					dotBtn, 
				equalBtn),
		),
	))

	w.ShowAndRun()
}