Arithmetic, Modulo & Increment Operators

In Plain English

C++ provides a full suite of mathematical operators: addition (+), subtraction (-), multiplication (*), division (/), modulo remainder (%), and fast increment/decrement (++ and --). Watch out for integer division!

The Mental Model

"Integer division (7 / 2) is like cutting a physical pizza between 2 people without fractional slices—you both get 3 whole slices, and the remaining 1 slice is discarded into the modulo trash bin (7 % 2 = 1)."

Deep Dive: How It Works

Basic Arithmetic: +, -, *, /, % (modulo).

The Integer Division Trap: In C++, dividing two integers drops the decimal completely: 7 / 2 results in 3, NOT 3.5! To get 3.5, at least one number must be a float or double (7.0 / 2).

Modulo Operator (%): Returns the integer remainder after division. 10 % 3 = 1. Perfect for checking if a number is even (num % 2 == 0).

Increment & Decrement: count++ increases by 1; count-- decreases by 1.

Compound Assignment: x += 5 is shorthand for x = x + 5 (also -=, *=, /=).

Syntax Blueprint

int sum = 10 + 5;     // 15
int div = 7 / 2;      // 3 (truncated!)
double exact = 7.0/2; // 3.5
int rem = 7 % 2;      // 1 (remainder)
x++;                  // Adds 1

Use 7.0 for decimal division and % for integer remainders.

Core Rules to Remember

Integer Division Quirk: Dividing two ints truncates (chops off) all decimal digits without rounding.

Modulo for Parity: num % 2 == 0 checks if a number is even; num % 2 != 0 checks if odd.

Operator Precedence: * and / calculate before + and - (PEMDAS order of operations).

Common Beginner Traps & How to Fix Them

Mistake:Writing double result = 5 / 2; and wondering why result is 2.0

Why it happens: 5 / 2 evaluates as integer math FIRST (yielding 2), and is then cast to 2.0.

How to fix: Write double result = 5.0 / 2; to trigger floating-point division.

Pro Tip: Use parentheses to make math calculations explicitly clear: int total = (price * count) + tax;.

Live Interactive Example

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Arithmetic and Modulo Math

C++ 20

Output Console

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How it works: Division calculates how many groups fit, and modulo calculates the remainder.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Calculate rectangle area and perimeter

Declare int width = 8; and int height = 5;
Calculate int area = width * height; and int perimeter = 2 * (width + height);
Print "Area: 40 | Perimeter: 26".

Sandbox Output

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