How to access a button using its name as a string in a for loop

You can do it in one line with LINQ

Controls.OfType<Button>().ToList().ForEach(b => b.Enabled = false);

VB (also via converter)

Controls.OfType(Of Button)().ToList().ForEach(Function(b) InlineAssignHelper(b.Enabled, False))

you can use following code :

foreach (Control ctrl in this.Controls)
            {
                if (ctrl is Button)
                {
                    ctrl.Enabled = true;
                }
            }

if its inside any container control , then try this :

foreach (Control Cntrl in this.Pnl.Controls)
            {
                if (Cntrl is Panel)
                {
                    foreach (Control C in Cntrl.Controls)
                        if (C is Button)
                        {
                            C.Enabled = true;
                        }
                }
            }

if want to implement in VB, then try this :

For Each Cntrl As Control In Me.Pnl.Controls
    If TypeOf Cntrl Is Panel Then
        For Each C As Control In Cntrl.Controls
            If TypeOf C Is Button Then
                C.Enabled = False
            End If
        Next
    End If
Next

for(int i =1;i<=25;i++)
{
    this.Controls["bt"+ i].Enable = True;
 //Or
    //yourButtonContainerObject.Controls["bt"+ i].Enable = True;
    // yourButtonContainerObject may be panel1, pane2 or Form, Depends where
   // your buttons are added. 'this' can be used in case of 'Form' only
}

Above code is valid only if you really have 25 buttonns and named as bt1,bt2,bt3...,bt25

       foreach (Control ctrl in yourButtonContainerObject.Controls)
        {
            if (ctrl is Button)
            {
                ctrl.Enabled = false;
            }
        }

Above code is better if you want to enable all the buttons in a particular container (Form or panel etc).