(Old) PS - Calculation

#include <stdio.h>

double x1, x2, x3, sum;
char t1[10], t11[10], t2[10], t22[10], t3[10], * stopstring;

// x1
if ((IsDlgButtonChecked(hDlg, IDC_CHECK1)))
{
    GetDlgItemText(hDlg, IDC_EDIT2, t1, 100);
    x1 = strtod(t1,&stopstring);
}
else
{
    x1 = 0;
}

// x2
if ((IsDlgButtonChecked(hDlg, IDC_CHECK2)))
{
    GetDlgItemText(hDlg, IDC_EDIT3, t2, 100);
    x2 = strtod(t2, &stopstring);
}
else
{
    x2 = 0;
}

// x3
if ((IsDlgButtonChecked(hDlg, IDC_CHECK3)))
{
    cbIndex = SendDlgItemMessage(hDlg, IDC_COMBO2, CB_GETCURSEL, 0, 0);
    if (cbIndex > -1)
    {
        SendDlgItemMessage(hDlg, IDC_COMBO2, CB_GETLBTEXT, cbIndex, (LPARAM)data);
    }
    x3 = strtod(data, &stopstring);
}
else
{
    x3 = 0;
}

// result
sum = x1 + x2 + x3;
sprintf_s(t22, "%6.3f", sum);
SetDlgItemText(hDlg, IDC_EDIT4, t22);