The CompareValidator control compares the value of one control to another, or to an explicit value in the control's ValueToCompare property. CompareValidator uses three key properties to perform its validation. ControlToValidate and ControlToCompare contain the values to compare. Operator defines the type of comparison to perform, for example, Equal or Not Equal. CompareValidator performs the validation by evaluating these properties as an expression, as shown in the following example.