praksa 1

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            int a;
            if (!int.TryParse(tb1.Text, out a))
            {
                MessageBox.Show("Greska! pogresan unos prvog broja");
            }
            else
            {
            int b;

                if (!int.TryParse(tb2.Text, out b))
            {
                MessageBox.Show("Greska! pogresan unos prvog broja");
            }
            else{
                if (cb1.SelectedItem == "+")
                {
                    tb3.Text = Convert.ToString(a + b);
                }
                else if (cb1.SelectedItem == "-")
                {
                    tb3.Text = Convert.ToString(a - b);
                }
                else if (cb1.SelectedItem == "*")
                {
                    tb3.Text = Convert.ToString(a * b);
                }
                else if (cb1.SelectedItem == "/")
                {
                    tb3.Text = Convert.ToString(a / b);
                }
                else
                {
                    MessageBox.Show("Niste odabrali operaciju");
                }
                }}
        }
    }
}