Problem Multi Form Application

public partial class MainForm : Form

    {

        public MainForm()

        {

            InitializeComponent();

        }

        //You are getting the error because you have declared Form variables with in the method

        //And trying to access them from other method

        //Variable for form1 is is out of scope in second method and similarly others

        //Declare the variables at class level to access it from all the methods

        Form1 SR;

        Form2 SCRI;

        Form3 CF;

        private void btn_Rechange_Click(object sender, EventArgs e)

        {

            //Check if the form1 already open/Exists, if exists get the form1 object else create a new form1 object           

            SR = (Form1) Application.OpenForms["Form1"];

            if (SR == null)

                SR = new Form1();

            SR.Show();

            //Check if form2 is already open/exists, if exists close

            SCRI = (Form2) Application.OpenForms["Form2"];

            if(SCRI != null)

            SCRI.Close();

            //You can also use Hide method

        //Check if form3 is already open/exists, if exists close

        CF = (Form3) Application.OpenForms["Form3"];

        if (CF != null)

            CF.Close();           

        }

        //Similarly for other forms also

        private void btn_CRI_Click_Click(object sender, EventArgs e)

        {

            SCRI = (Form2) Application.OpenForms["Form2"];

            if (SCRI == null)

                SCRI = new Form2();

            SCRI.Show();

            SR = (Form1) Application.OpenForms["Form1"];

            if (SR != null)

                SR.Close();

            CF = (Form3) Application.OpenForms["Form3"];

            if (CF != null)

                CF.Close();

        }

        private void btn_Config_Click(object sender, EventArgs e)

        {

            CF = (Form3) Application.OpenForms["Form3"];

            if (CF == null)

                CF = new Form3();

            CF.Show();

            SR = (Form1) Application.OpenForms["Form1"];

            if (SR != null)

                SR.Close();

            SCRI = (Form2) Application.OpenForms["Form2"];

            if (SCRI != null)

                SCRI.Close();

        }

    }