C# 4.0 Programming: Logical Operators

	Logical Operators

Introduction

A comparison is an operation used to get the Boolean result of two values one checked against the other. Such a comparison is performed between two values of the same type.

Equality

To compare two variables for equality, use the = operator. Its syntax is:

Value1 = Value2

The equality operation is used to find out whether two variables (or one variable and a constant) hold the same value. From our syntax, the value of Value1 would be compared with the value of Value2. If Value1 and Value2 hold the same value, the comparison produces a True result. If they are different, the comparison renders false or 0.

The comparison for equality

Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim IsFullTime As Boolean

        MsgBox("Is Employee Full Time? " & IsFullTime)

        IsFullTime = True
        MsgBox("Is Employee Full Time? " & IsFullTime)
        Return 0
    End Function

End Module

This would produce:

Inequality <>

As opposed to checking for equality, you may instead want to know whether two values are different. The operator used to perform this comparison is <> and its formula is:

Variable1 <> Variable2

The comparison for inequality

If the operands on both sides of the operator are the same, the comparison renders false. If both operands hold different values, then the comparison produces a true result. This also shows that the equality = and the inequality <> operators are opposite.

Here is an example:

Module Exercise

    Public Function IsDifferent(ByVal Value1 As Integer,
                                ByVal Value2 As Integer) As Boolean
        Return (Value1 <> Value2)
    End Function

    Public Function Main() As Integer
        Dim a%, b%
        Dim Result As Boolean

        a% = 12 : b% = 48
        Result = IsDifferent(a%, b%)

        MsgBox("The resulting comparison of 12 <> 48 is " & Result)
        Return 0
    End Function

End Module

This would produce:

Comparison for Inequality

A Lower Value <

To find out whether one value is lower than another, use the < operator. Its syntax is:

Value1 < Value2

The value held by Value1 is compared to that of Value2. As it would be done with other operations, the comparison can be made between two variables, as in Variable1 < Variable2. If the value held by Variable1 is lower than that of Variable2, the comparison produces a True.

Flowchart: Less Than

Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim PartTimeSalary, ContractorSalary As Double
        Dim IsLower As Boolean

        PartTimeSalary = 20.15
        ContractorSalary = 22.48
        IsLower = PartTimeSalary < ContractorSalary

        MsgBox("Part Time Salary:  " & PartTimeSalary & vbCrLf &
               "Contractor Salary: " & ContractorSalary & vbCrLf &
               "Is PartTimeSalary < ContractorSalary? " & IsLower)

        PartTimeSalary = 25.55
        ContractorSalary = 12.68
        IsLower = PartTimeSalary < ContractorSalary

        MsgBox("Part Time Salary:  " & PartTimeSalary & vbCrLf &
               "Contractor Salary: " & ContractorSalary & vbCrLf &
               "Is PartTimeSalary < ContractorSalary? " & IsLower)
        Return 0
    End Function

End Module

This would produce:

Equality and Lower Value <=

The previous two operations can be combined to compare two values. This allows you to know if two values are the same or if the first is less than the second. The operator used is <= and its syntax is:

Value1 <= Value2

The <= operation performs a comparison as any of the last two. If both Value1 and VBalue2 hold the same value, result is true or positive. If the left operand, in this case Value1, holds a value lower than the second operand, in this case Value2, the result is still true:

Less than or equal to

Greater Value >

When two values of the same type are distinct, one of them is usually higher than the other. VBasic provides a logical operator that allows you to find out if one of two values is greater than the other. The operator used for this operation uses the > symbol. Its syntax is:

Value1 > Value2

Both operands, in this case Value1 and Value2, can be variables or the left operand can be a variable while the right operand is a constant. If the value on the left of the > operator is greater than the value on the right side or a constant, the comparison produces a True value. Otherwise, the comparison renders False or null:

Greater Than

Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim PartTimeSalary, ContractorSalary As Double
        Dim IsLower As Boolean

        PartTimeSalary = 20.15
        ContractorSalary = 22.48
        IsLower = PartTimeSalary > ContractorSalary

        MsgBox("Part Time Salary:  " & PartTimeSalary & vbCrLf &
               "Contractor Salary: " & ContractorSalary & vbCrLf &
               "Is PartTimeSalary > ContractorSalary? " & IsLower)

        PartTimeSalary = 25.55
        ContractorSalary = 12.68
        IsLower = PartTimeSalary > ContractorSalary

        MsgBox("Part Time Salary:  " & PartTimeSalary & vbCrLf &
               "Contractor Salary: " & ContractorSalary & vbCrLf &
               "Is PartTimeSalary > ContractorSalary? " & IsLower)
        Return 0
    End Function

End Module

This would produce:

Greater or Equal Value >=

The greater than or the equality operators can be combined to produce an operator as follows: >=. This is the "greater than or equal to" operator. Its syntax is:

Value1 >= Value2

A comparison is performed on both operands: Value1 and Value2. If the value of Value1 and that of Value2 are the same, the comparison produces a True value. If the value of the left operand is greater than that of the right operand, the comparison still produces True. If the value of the left operand is strictly less than the value of the right operand, the comparison produces a False result:

Greater Than Or Equal