How to use local variables from loop and assign them to equations from other structs

private void ParametersChanged(object sender, EventArgs e)
{
    if (AreArgumentsValid() && klasaBetonaComboBox.SelectedItem != null)
    {

        var _dMed = Convert.ToDouble(MomentSavijanjaMed.Text);                   
        var  _dh = Convert.ToDouble(VisinaPresjekaH.Text);
        var _db = Convert.ToDouble(SirinaPresjekaB.Text);
        var _dd1 = Convert.ToDouble(UdaljenostArmD1.Text);
        var _dd = _dh - _dd1;
        var _dFck = Convert.ToDouble(fck.Text);
        var _gamaC = 1.50;
        gamaCRezultat.Text = _gamaC.ToString();
        var dFcd =  _dFck /_gamaC;
        FcdRezultat.Text = dFcd.ToString();

        var _dMiSd = _dMed * 1000 / (_dd * _dd * _db * dFcd);

        rezultat.Text = _dMiSd.ToString("F4");
    }

from here i need to use variable _dMiSd and _dd in next struct.

private void deformacijaCelikaComboBox_SelectedIndexChanged(object sender, EventArgs e)
{
    double epsilonC2;
    double ksiRacunski;
    double zetaRacunska;
    double kARacunski;
    double epsilonC2pretpostavka;
    double miSdCrtica;
    double alphaVRacunski;
    double selectedDeformacija = ((NovaDeformacijaArmature)deformacijaCelikaComboBox.SelectedItem).epsilonCelika;
    double zeta;
    double ksi;
    double xNeutralnaOs;
    double zKrakSila;

    if (selectedDeformacija == 20.0)
    {
        for (epsilonC2pretpostavka = 0.01; epsilonC2pretpostavka <=3.5 ; epsilonC2pretpostavka += 0.01)
        {
            ksiRacunski = epsilonC2pretpostavka / (selectedDeformacija + epsilonC2pretpostavka);

            if (epsilonC2pretpostavka <= 2)
            {
                kARacunski = 8 - epsilonC2pretpostavka / (4 * (6 - epsilonC2pretpostavka));
                alphaVRacunski = (epsilonC2pretpostavka * (6 - epsilonC2pretpostavka)) / 12;
            }
            else if (epsilonC2pretpostavka <= 3.5)
            {
                kARacunski = (epsilonC2pretpostavka * (3 - epsilonC2pretpostavka - 4) + 2) / (2 * epsilonC2pretpostavka * (3 * epsilonC2pretpostavka - 2));
                alphaVRacunski = (3 * epsilonC2pretpostavka - 2) / (3 * epsilonC2pretpostavka);
            }

            zetaRacunska = 1 - (kARacunski * ksiRacunski);
            miSdCrtica = 0.85 * alphaVRacunski * ksiRacunski * zetaRacunska;

            if (Math.Abs(miSdCrtica-_dMiSd)<0.0001)
            {
                epsilonC2pretpostavka = epsilonC2;
                zetaRacunska = zeta;
                ksiRacunski = ksi;
                xNeutralnaOs = ksi * _dd;
                zKrakSila = zeta * _dd;
            }

here i got for loop as you see. Inside of it i have if case which would give me values for variables kAracunski and alphaVracunski.

When i get them from calculation i want to use them for calculation miSdCrtica.

After that i want to check does their difference satisfy given condition.

I get an error:

"Variables does not exist in current context (for _dMiSd and _dd).

And error

"Use of unassigned variable alphaVRacunski and zetaRacunski.

How to link them up together?