C#

foreach(Control control in Controls){
    if(control is Label){
        ((Label)control).Text = "Something";
    }
}

foreach (Control control in Controls)
    {
    if (control is Label && label.Name.StartsWith("labelNamePrefixToModifyAsAGroup"))
        {
        ((Label)control).Text = "Something";
        }
    }

foreach (Control c in Controls) if (c.Name.StartsWith("labela")) c.Text = "Something";

private void SetLabelText(ref Label label, string text)
{
    label.Text = text;
}

private void SomeFunction()
{
    SetLabelText(ref label1, "something1");
    SetLabelText(ref label2, "something2");
    SetLabelText(ref label3, "something3");
}

for (int i=1;1<4;i++){
 this.Controls[string.Concat("labela", i.ToString())].Text = "something";
}

class Form1
{
    IEnumerable<Control> summingLabels; 

    public Form1()
    {
	InitializeComponent();
	
	summingLabels =
		from c in Controls.Cast<Control>().AsQueryable()
		where c.Name.StartsWith("sumLabel")
		select c;

	// later on, when you need them
	foreach(Control l in summingLabels)
		l.Text = l.Name;
    }
}

I are Troll

foreach (Control l in Controls.Cast<Control>().Where(c => c.Name.StartsWith("sumLabel")))
	l.Text = l.Name;

class Form1
{
    IEnumerable<Label> summingLabels; 
    public Form1()
    {
    	InitializeComponent();
	
    	summingLabels =
    		from c in Controls.Cast<Control>().AsQueryable()
    		where c.GetType() == typeof(Label)
    		&& c.Name.StartsWith("label")
    		select c as Label;
    
    	// later on, when you need them
    	foreach(Label l in summingLabels)
    		l.Text = l.Location.ToString();
    }
}

I are Troll

summingLabels =
    		from c in Controls.OfType<Label>()
    		where c.Name.StartsWith("label")
    		select c;
    
    	// later on, when you need them
    	foreach(Label l in summingLabels)
    		l.Text = l.Location.ToString();

Label[] labels = { labela1, labela2, labela3 };