6.5.1 Arithmetic operators

Arithmetic Operators in Programs

You already know what arithmetic operators do from Topic 1. The focus here is writing programs that use them correctly — choosing the right operator for the task, combining them in expressions, and understanding the results in Python's type system.

Operator	Operation	Python	C#	VB.NET
Addition	Sum	`+`	`+`	`+`
Subtraction	Difference	`-`	`-`	`-`
Multiplication	Product	`*`	`*`	`*`
Division	Real result	`/`	`/` (int ÷ int = int)	`/`
Integer division	Floor quotient	`//`	`/` (int operands)
Modulus	Remainder	`%`	`%`	`Mod`
Exponentiation	Power	`**`	`Math.Pow()`	`^`

Note: in Python, / always gives a real (float) result even for two integers. Use // for integer division.

Worked Example: Bill Calculator

subtotal = float(input("Subtotal (£): "))
VAT_RATE = 0.20

vat      = subtotal * VAT_RATE          # multiplication
total    = subtotal + vat               # addition
saving   = total - subtotal             # subtraction (same as vat here)
per_head = total / 4                    # division — real result
whole    = total // 1                   # integer division — floor
pence    = round((total % 1) * 100)     # modulus — pence remainder
tip      = subtotal ** 0.5              # exponentiation — square root trick

print("VAT:      £" + str(round(vat, 2)))
print("Total:    £" + str(round(total, 2)))
print("Per head: £" + str(round(per_head, 2)))
print("Pence:    " + str(pence) + "p")
print("Tip idea: £" + str(round(tip, 2)))

double subtotal = double.Parse(Console.ReadLine());
const double VAT_RATE = 0.20;

double vat      = subtotal * VAT_RATE;
double total    = subtotal + vat;
double perHead  = total / 4;
int    whole    = (int)(total);
int    pence    = (int)Math.Round((total % 1) * 100);
double tip      = Math.Pow(subtotal, 0.5);

Console.WriteLine("VAT:      £" + Math.Round(vat, 2));
Console.WriteLine("Total:    £" + Math.Round(total, 2));
Console.WriteLine("Per head: £" + Math.Round(perHead, 2));
Console.WriteLine("Pence:    " + pence + "p");
Console.WriteLine("Tip idea: £" + Math.Round(tip, 2));

Dim subtotal As Double = Double.Parse(Console.ReadLine())
Const VAT_RATE As Double = 0.20

Dim vat      As Double = subtotal * VAT_RATE
Dim total    As Double = subtotal + vat
Dim perHead  As Double = total / 4
Dim whole    As Integer = CInt(Int(total))
Dim pence    As Integer = CInt(Math.Round((total Mod 1) * 100))
Dim tip      As Double = subtotal ^ 0.5

Console.WriteLine("VAT:      £" & Math.Round(vat, 2))
Console.WriteLine("Total:    £" & Math.Round(total, 2))
Console.WriteLine("Per head: £" & Math.Round(perHead, 2))
Console.WriteLine("Pence:    " & pence & "p")
Console.WriteLine("Tip idea: £" & Math.Round(tip, 2))

The // and % Pair in Practice

Integer division and modulus are complementary — together they decompose a value into quotient and remainder. Common uses: converting seconds to minutes/seconds, checking even/odd, cycling through a fixed range.

# Python — time conversion using // and %
total_seconds = int(input("Enter seconds: "))
minutes = total_seconds // 60
seconds = total_seconds % 60
print(str(minutes) + "m " + str(seconds) + "s")

# Even/odd check
n = int(input("Enter a number: "))
if n % 2 == 0:
    print(n, "is even")
else:
    print(n, "is odd")

# Cycling 0-4 using modulus
for i in range(10):
    print(i % 5, end=" ")   # 0 1 2 3 4 0 1 2 3 4

Key Takeaways

Python / always returns a float; use // for integer (floor) division.
% gives the remainder — useful for even/odd, time conversion, cycling.
** (Python) / ^ (VB.NET) / Math.Pow() (C#) for exponentiation.
Use named constants (VAT_RATE) rather than magic numbers in calculations.