Boolean operators

Boolean Operators

A Boolean operator combines or modifies Boolean values (True / False) to produce a new Boolean result. AQA requires three operators: NOT, AND, and OR. You must be able to use them individually and in combination inside selection (IF) and iteration (WHILE) conditions.

Operator	Meaning	AQA pseudocode	Python	VB.NET	C#
NOT	Inverts the value	`NOT`	`not`	`Not`	`!`
AND	True only if both sides are True	`AND`	`and`	`And`	`&&`
OR	True if at least one side is True	`OR`	`or`	`Or`	`\|\|`

Operators in Conditions

The tabs below show each operator used in a realistic program. Notice how combining operators with relational expressions lets a single condition capture complex real-world rules.

AND requires every condition to be True. Use it when a result is only valid if all criteria are met simultaneously - e.g. a user must be logged in and have the correct role to access a page.

AQA pseudocode:

IF age >= 18 AND hasTicket = TRUE THEN
    OUTPUT "Entry permitted"
ELSE
    OUTPUT "Entry refused"
ENDIF

# Python
age = int(input("Age: "))
has_ticket = input("Ticket? (yes/no): ") == "yes"
if age >= 18 and has_ticket:          # AND -- both must be True
    print("Entry permitted")
else:
    print("Entry refused")

' VB.NET
' Dim age As Integer = CInt(Console.ReadLine())
' Dim hasTicket As Boolean = (Console.ReadLine() = "yes")
' If age >= 18 And hasTicket Then     ' And -- both must be True
'     Console.WriteLine("Entry permitted")
' Else
'     Console.WriteLine("Entry refused")
' End If

// C#
// int age = int.Parse(Console.ReadLine());
// bool hasTicket = Console.ReadLine() == "yes";
// if (age >= 18 && hasTicket)         // && -- both must be True
//     Console.WriteLine("Entry permitted");
// else
//     Console.WriteLine("Entry refused");

OR requires at least one condition to be True. Use it when any of several alternatives should trigger the same outcome - e.g. a discount applies if the customer is a student or a senior citizen.

AQA pseudocode:

IF isStudent = TRUE OR isSenior = TRUE THEN
    OUTPUT "Discount applied"
ELSE
    OUTPUT "Full price"
ENDIF

# Python
is_student = input("Student? (yes/no): ") == "yes"
is_senior  = input("Senior?  (yes/no): ") == "yes"
if is_student or is_senior:           # OR -- at least one must be True
    print("Discount applied")
else:
    print("Full price")

' VB.NET
' Dim isStudent As Boolean = (Console.ReadLine() = "yes")
' Dim isSenior  As Boolean = (Console.ReadLine() = "yes")
' If isStudent Or isSenior Then       ' Or -- at least one must be True
'     Console.WriteLine("Discount applied")
' Else
'     Console.WriteLine("Full price")
' End If

// C#
// bool isStudent = Console.ReadLine() == "yes";
// bool isSenior  = Console.ReadLine() == "yes";
// if (isStudent || isSenior)          // || -- at least one must be True
//     Console.WriteLine("Discount applied");
// else
//     Console.WriteLine("Full price");

NOT inverts a Boolean value. It is often used in WHILE conditions and can be combined with AND or OR to form complex conditions. Here a login loop runs while the password is wrong and there are attempts remaining:

AQA pseudocode:

WHILE NOT correct AND attempts < 3 DO
    INPUT password
    IF password = "secret" THEN
        correct ← TRUE
    ENDIF
    attempts ← attempts + 1
ENDWHILE

# Python
correct  = False
attempts = 0
while not correct and attempts < 3:   # NOT + AND combined
    password = input("Password: ")
    if password == "secret":
        correct = True
    attempts += 1
print("Access granted" if correct else "Locked out")

' VB.NET
' Dim correct  As Boolean = False
' Dim attempts As Integer = 0
' Do While Not correct And attempts < 3   ' Not + And combined
'     Dim password As String = Console.ReadLine()
'     If password = "secret" Then correct = True
'     attempts += 1
' Loop
' Console.WriteLine(If(correct, "Access granted", "Locked out"))

// C#
// bool correct  = false;
// int  attempts = 0;
// while (!correct && attempts < 3)    // ! + && combined
// {
//     string password = Console.ReadLine();
//     if (password == "secret") correct = true;
//     attempts++;
// }
// Console.WriteLine(correct ? "Access granted" : "Locked out");

Key Takeaways

AND returns True only when both operands are True. One False side makes the whole expression False.
OR returns True when at least one operand is True. Both sides must be False for OR to return False.
NOT inverts a single Boolean value: NOT True gives False, and NOT False gives True.
Operators differ across languages: Python uses and / or / not (keywords); C# uses && / || / ! (symbols); VB.NET uses And / Or / Not.
Boolean operators can be combined with relational operators to build complex conditions inside IF statements and WHILE loops.