How to use C# string Contains

using System;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string str = null;
            str = "CSharp TOP 10 BOOKS";
            if (str.Contains("TOP") == true)
            {
                MessageBox.Show("The string Contains() 'TOP' ");
            }
            else
            {
                MessageBox.Show("The String does not Contains() 'TOP'");
            } 
        }
    }
}

When you run the C# program you will get the MessageBox with message 

"The string Contains() 'TOP' "