CheckRadioButton is a function in the user32.dll library that is part of the Microsoft Windows operating system. It is used to select a radio button in a group of radio buttons.

A radio button is a graphical control element that allows the user to choose one option from a set of mutually exclusive options. Radio buttons are typically used when there are a small number of options to choose from, and it is not practical to present them as a dropdown list or list box.

The CheckRadioButton function is called with the handle to the parent window and the identifier of the radio button to be selected. It can also be passed a value indicating whether the other radio buttons in the group should be deselected.

For example, to select the third radio button in a group with the identifier IDC_RADIO3, you could use the following code: