calculator | Simple calculator built with React | Apps library

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({ Key? key }) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primaryColor:Colors.pink[300],
      ),
      home: Calculator(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class Calculator extends StatefulWidget {
  const Calculator({ Key? key }) : super(key: key);

  @override
  _CalculatorState createState() => _CalculatorState();
}

class _CalculatorState extends State {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Calculator'),
        centerTitle: true,
      ),
     body:Container(
       child: Column(
         children: [
           Expanded(
             child:Container(
               padding: EdgeInsets.all(10.0),
               alignment: Alignment.bottomRight,
               child:Text(text,
               style: TextStyle(
                 fontSize: 50.0,
                 fontWeight: FontWeight.w500,
               ),
               ),
             )
           ),
             Row(
               children: [ 
                 customElevatedButton('9',),
                 customElevatedButton('8',),
                 customElevatedButton('7',), 
                 customElevatedButton('+',),              
               ],    
             ),
             Row(
               children: [ 
                 customElevatedButton('6',),
                 customElevatedButton('5',),
                 customElevatedButton('4',), 
                 customElevatedButton('-',),              
               ],              
             ),
             Row(
               children: [ 
                 customElevatedButton('3'),
                 customElevatedButton('2'),
                 customElevatedButton('1'), 
                 customElevatedButton('X'),              
               ],               
             ),
             Row(
               children: [ 
                 customElevatedButton('C',),
                 customElevatedButton('0',),
                 customElevatedButton('=',), 
                 customElevatedButton('/',),              
               ],              
             ),
         ],
       ),
     )
    );   
  }

  Widget customElevatedButton(num) {
    return Expanded(
      child: RaisedButton(  
                padding:EdgeInsets.all(25.0),
                color:Colors.pink[100] ,             
                onPressed:(){
                  operation(num);
                },
                child:Text(num,
                style: TextStyle(fontSize: 40.0),             
                ),
                ),
    );
  }
String text='';
void operation(clickedButt)
{
  String result;
  int first,second;
  String opp;
  if(clickedButt=='C'){
    result='';
    text='';
  }
  else if(clickedButt=='+'||clickedButt=='-'||clickedButt=='X'||clickedButt=='/'){
    first=int.parse(text);
    result='';
    opp=clickedButt;
  }
  else if(clickedButt=='='){
    second=int.parse(text);
    result='';
    if(opp=='+'){
      result=(first+second).toString();
    }
    else if(opp=='-'){
      result=(first-second).toString();
    }
    else if(opp=='*'){
      result=(first*second).toString();
    }
    else if(opp=='/'){
      result=(first/second).toString();
    }
    else{
      result=int.parse(text+clickedButt).toString();
    }
    
  }
  else{
    result=text+clickedButt;
  }
  setState(() {
    text=result;
  });
}



}