How to select the listbox values in windows phone 7?

I'm doing one sample app for birthday calender. In that I'm using three listbox control such as date , month and year. Using listboxitem I added data into it.

    <ListBox Height="56" HorizontalAlignment="Left" Margin="243,171,0,0" Name="listBox1" VerticalAlignment="Top" Width="207">
            <ListBoxItem Content="01" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="02" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5"/>
            <ListBoxItem Content="03" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="04" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="05" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="06" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="07" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="08" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />开发者_StackOverflow中文版
            <ListBoxItem Content="09" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="10" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="11" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="12" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="13" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="14" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="15" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="16" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="17" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="18" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="19" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="20" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="21" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="22" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="23" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="24" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="25" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="26" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="27" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5"/>
            <ListBoxItem Content="28" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="29" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="30" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
            <ListBoxItem Content="31" HorizontalContentAlignment="Center" IsSelected="True" VerticalContentAlignment="Center" FontSize="32" FontWeight="Bold" FontFamily="Segoe WP Bold" BorderThickness="5" />
    </ListBox>

so, i want to select those listbox values and i have to add(Eg: 24-MAR-1988 means = 24+03+88). i got index value.

int a = int.Parse((listBox1.SelectedIndex+1).ToString());

I coudn't get selected value:

string b = listBox1.SelectedItem.ToString(); MessageBox.Show(b);

I really recommend you use Silverlight Toolkit for Windows Phone. It has a DatePicker control.

If you really want to use your own ComboBox controls, I recommend you at least use DateTime type available in C# to make things easier.