> For the complete documentation index, see [llms.txt](https://alham-rizvi.gitbook.io/alhamrizvi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alham-rizvi.gitbook.io/alhamrizvi/c++-notes/06.-arithmetic-operators.md).

# 06. Arithmetic Operators

Arithmetic operators let you do math on numeric values.

| Operator | Meaning             | Example | Result                        |
| -------- | ------------------- | ------- | ----------------------------- |
| `+`      | Addition            | `5 + 2` | `7`                           |
| `-`      | Subtraction         | `5 - 2` | `3`                           |
| `*`      | Multiplication      | `5 * 2` | `10`                          |
| `/`      | Division            | `5 / 2` | `2` (int division truncates!) |
| `%`      | Modulus (remainder) | `5 % 2` | `1`                           |

```cpp
#include <iostream>

int main() {
    int a = 10;
    int b = 3;

    std::cout << "a + b = " << a + b << '\n';
    std::cout << "a - b = " << a - b << '\n';
    std::cout << "a * b = " << a * b << '\n';
    std::cout << "a / b = " << a / b << '\n'; // 3, not 3.33
    std::cout << "a % b = " << a % b << '\n'; // 1 (remainder)

    return 0;
}
```

***

### ⚠️ The #1 beginner trap: integer division

If **both** operands are `int`, the result is an `int` — any decimal part gets chopped off (not rounded).

```cpp
#include <iostream>

int main() {
    int a = 7;
    int b = 2;

    std::cout << a / b << '\n'; // prints 3, NOT 3.5

    return 0;
}
```

**Fix:** make at least one operand a `double`.

```cpp
#include <iostream>

int main() {
    int a = 7;
    int b = 2;

    double result = (double)a / b; // cast a to double first
    std::cout << result << '\n';   // prints 3.5

    return 0;
}
```

***

### Increment / Decrement (`++` and `--`)

Shortcuts for adding or subtracting 1.

```cpp
#include <iostream>

int main() {
    int count = 5;

    count++; // same as count = count + 1
    std::cout << count << '\n'; // 6

    count--; // same as count = count - 1
    std::cout << count << '\n'; // 5

    return 0;
}
```

**Pre vs post increment** (a classic gotcha):

```cpp
int x = 5;
std::cout << x++ << '\n'; // prints 5, THEN increments (x becomes 6)
std::cout << ++x << '\n'; // increments FIRST (x becomes 7), THEN prints 7
```

***

### Compound assignment operators

Shorthand for "do the math, then assign it back."

| Operator | Same as     |
| -------- | ----------- |
| `a += 5` | `a = a + 5` |
| `a -= 5` | `a = a - 5` |
| `a *= 5` | `a = a * 5` |
| `a /= 5` | `a = a / 5` |
| `a %= 5` | `a = a % 5` |

```cpp
#include <iostream>

int main() {
    int score = 10;

    score += 5; // score is now 15
    score *= 2; // score is now 30

    std::cout << score << '\n';

    return 0;
}
```

***

### More cool examples

#### 1. A simple calculator

```cpp
#include <iostream>

int main() {
    double num1 = 12;
    double num2 = 5;

    std::cout << "Sum: " << num1 + num2 << '\n';
    std::cout << "Difference: " << num1 - num2 << '\n';
    std::cout << "Product: " << num1 * num2 << '\n';
    std::cout << "Quotient: " << num1 / num2 << '\n';

    return 0;
}
```

#### 2. Checking even or odd using `%`

```cpp
#include <iostream>

int main() {
    int number = 17;

    if (number % 2 == 0) {
        std::cout << number << " is even\n";
    } else {
        std::cout << number << " is odd\n";
    }

    return 0;
}
```

#### 3. Splitting seconds into minutes and seconds

```cpp
#include <iostream>

int main() {
    int totalSeconds = 125;

    int minutes = totalSeconds / 60; // int division: whole minutes
    int seconds = totalSeconds % 60; // remainder: leftover seconds

    std::cout << minutes << "m " << seconds << "s\n"; // 2m 5s

    return 0;
}
```

#### 4. A running total with compound operators

```cpp
#include <iostream>

int main() {
    int total = 0;

    total += 100; // deposit
    total -= 30;  // withdrawal
    total += 50;  // deposit

    std::cout << "Final balance: " << total << '\n'; // 120

    return 0;
}
```

***

### Quick Recap

* Basic operators: `+ - * / %`
* **Integer division truncates** — cast to `double` if you need decimals.
* `++` / `--` increment or decrement by 1 (watch pre vs post placement).
* Compound operators (`+=`, `-=`, etc.) shorten `a = a op b` to `a op= b`.


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