Calculator

gistfile1.cs

using System;
using System.CodeDom.Compiler;
using System.Drawing;
using System.Windows.Forms;
using Microsoft.CSharp;

namespace BitCalculator
{
    public partial class MainForm : Form
    {
        private delegate string Calculate();

        public MainForm()
        {
            InitializeComponent();
        }

        private void tbInput_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Enter && !string.IsNullOrEmpty(tbInput.Text.Trim()))
            {
                try
                {
                    tbOutput.ForeColor = Color.Cyan;
                    tbOutput.Text      = (Compile<Calculate>(tbInput.Text) as Calculate)();
                }
                catch (Exception ex)
                {
                    tbOutput.ForeColor = Color.Red;
                    tbOutput.Text      = ex.Message;
                }
            }
        }

        private Delegate Compile<T>(string code)
        {
            string compileStr = string.Format(@"
            using System;
            class Calculator 
            {{
                public static string Invoke() 
                {{ 
                    return ({0}).ToString(); 
                }} 
            }}", code);

            CompilerParameters compilerParameters = new CompilerParameters();
            compilerParameters.GenerateInMemory   = true;
            CompilerResults compileResults        = new CSharpCodeProvider().CompileAssemblyFromSource(compilerParameters, compileStr);
            
            if (compileResults.Errors.Count > 0)
                throw new Exception("Error");
            else 
                return Delegate.CreateDelegate(typeof(T), compileResults.CompiledAssembly.GetType("Calculator").GetMethod("Invoke")); 
        }
    }
}