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Merge pull request #16 from khd33j/feature
Feature: Add Python notes
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‎Python/Basic Operators.md‎

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# Basic Operators
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## Table of Contents
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- **[Arithmetic Operators](#arithmetic-operators)**
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- **[Comparison Operators](#comparison-operators)**
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- **[Logical Operators](#logical-operators)**
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- **[Operator Precedence](#operator-precedence)**
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- **[Highest to Lowest Precendence:](#highest-to-lowest-precendence))**
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---
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## Arithmetic Operators
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Arithmetic operators perform mathematical operations on numbers (integers, floats).
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| Operator | Symbol | Description | Example |
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|:----------|:-------|:------------|:--------|
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| **Addition** | `+` | Adds two operands | `3 + 2 = 5` |
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| **Subtraction** | `-` | Subtracts second operand from first | `5 - 2 = 3` |
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| **Multiplication** | `*` | Multiplies two operands | `3 * 2 = 6` |
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| **Division** | `/` | Divides first operand by second, returns float | `5 / 2 = 2.5` |
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| **Modulus** | `%` | Returns remainder of division | `5 % 2 = 1` |
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| **Floor Division** | `//` | Divides first operand by second, returns integer (floor) | `5 // 2 = 2` |
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| **Exponentiation** | `**` | Raises first operand to the power of second | `3 ** 2 = 9` |
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**Example:**
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```python
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a = 10
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b = 3
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print(a + b) # 13
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print(a - b) # 7
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print(a * b) # 30
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print(a / b) # 3.3333333333333335
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print(a % b) # 1
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print(a // b) # 3
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print(a ** b) # 1000
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```
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---
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## Comparison Operators
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Comparison operators are used to compare two values. They return either `True` or `False`.
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| Operator | Symbol | Description | Example |
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|:----------|:-------|:------------|:--------|
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| **Equal to** | `==` | Checks if two values are equal | `3 == 3` → True |
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| **Not equal to** | `!=` | Checks if two values are not equal | `3 != 2` → True |
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| **Greater than** | `>` | Checks if left operand is greater | `5 > 3` → True |
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| **Less than** | `<` | Checks if left operand is smaller | `2 < 5` → True |
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| **Greater than or equal to** | `>=` | Checks if left operand is greater or equal | `5 >= 5` → True |
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| **Less than or equal to** | `<=` | Checks if left operand is smaller or equal | `3 <= 5` → True |
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**Example:**
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```python
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x = 5
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y = 3
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print(x == y) # False
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print(x != y) # True
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print(x > y) # True
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print(x < y) # False
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print(x >= y) # True
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print(x <= y) # False
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```
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---
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## Logical Operators
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Logical operators combine multiple conditions to return a single boolean result. They’re often used with comparison operators.
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| Operator | Symbol | Description | Example |
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|:----------|:-------|:------------|:--------|
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| **AND** | `and` | True if both conditions are true | `True and False` → False |
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| **OR** | `or` | True if at least one condition is true | `True or False` → True |
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| **NOT** | `not` | Negates the condition (True to False, vice versa) | `not True` → False |
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**Example:**
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```python
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a = 5
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b = 3
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c = 8
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print(a > b and c > a) # True, both conditions are True
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print(a > b or b > c) # True, one condition is True
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print(not (a > b)) # False, as a > b is True, but `not` negates it
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```
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---
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## Operator Precedence
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Operator precedence determines the order in which operations are performed.
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Operators with higher precedence are evaluated first. If operators have the same precedence, they are evaluated from left to right.
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### Highest to Lowest Precendence:
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1. **Exponentiation:** **
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2. **Unary Operators:** +, - (positive, negative)
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3. **Multiplication, Division, Modulus, Floor Division:** *, /, %, //
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4. **Addition, Subtraction:** +, -
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5. **Comparison Operators:** <, <=, >, >=
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6. **Equality Operators:** ==, !=
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7. **Logical NOT:** not
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8. **Logical AND:** and
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9. **Logical OR:** or
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**Example of operator precendence:**
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```python
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result = 5 + 3 * 2 ** 2 - 4 / 2
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# Step-by-step evaluation:
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# 1. 2 ** 2 = 4
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# 2. 3 * 4 = 12
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# 3. 4 / 2 = 2
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# 4. 5 + 12 = 17
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# 5. 17 - 2 = 15
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print(result) # Output: 15
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```
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- **Using parentheses to override precedence:** Parentheses `()` can be used to explicitly control the order of evaluation.
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```python
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result = (5 + 3) * (2 ** 2) - (4 / 2)
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print(result) # Output: 30.0
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```

‎Python/Control Flow.md‎

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# Control Flow
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## Table of Contents
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- **[Basic if-else Conditions](#basic-if-else-conditions)**
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- **[Nested and Multiple Conditions (elif)](#nested-and-multiple-conditions)**
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- **[Logical Expressions in Control Flow](#logical-expressions-in-control-flow)**
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- **[Operators](#operators)**
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- **[Use Case Examples](#use-case-examples)**
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- **[Ternary Expressions](#ternary-expressions)**
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---
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## Basic if-else Conditions
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The `if` statement allows you to execute a block of code only if a specified condition is true. The `else` statement provides an alternative block of code if the condition is false.
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**Syntax:**
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```python
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if condition:
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# Code to execute if condition is true
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else:
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# Code to execute if condition is false
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```
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**Example:**
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```python
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age = 18
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if age >= 18:
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print("You are eligible to vote.")
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else:
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print("You are not eligible to vote.")
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```
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Here, the code checks if `age` is greater than or equal to 18. If true, it prints a message about eligibility. If false, it provides an alternate message.
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---
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## Nested and Multiple Conditions
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Python allows you to nest `if` statements within each other for more complex conditions or use `elif` (short for “else if”) for multiple conditions.
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**Syntax:**
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```python
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if condition1:
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# Code for condition1
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elif condition2:
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# Code for condition2
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else:
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# Code if neither condition1 nor condition2 is true
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```
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**Example of `elif`:**
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```python
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score = 85
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if score >= 90:
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print("Grade: A")
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elif score >= 80:
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print("Grade: B")
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elif score >= 70:
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print("Grade: C")
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else:
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print("Grade: D")
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```
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This code assigns a grade based on `score`. It checks each condition in order, and once a true condition is found, the corresponding block is executed, skipping any remaining conditions.
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**Example of nested conditions:**
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```python
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age = 20
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has_permission = True
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if age >= 18:
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if has_permission:
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print("Access granted.")
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else:
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print("Permission denied.")
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else:
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print("Access denied due to age.")
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```
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Here, `has_permission` is checked only if the first condition (`age >= 18`) is true. This allows for handling complex scenarios with dependencies.
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---
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## Logical Expressions in Control Flow
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Logical expressions use operators (`and`, `or`, `not`) to combine multiple conditions in a single `if` statement, enhancing flexibility.
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### Operators
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- `and`: Evaluates to true if both conditions are true.
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- `or`: Evaluates to true if at least one condition is true.
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- `not`: Inverts the boolean value of a condition.
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### Use Cases Examples
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- **Example 1:**
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```python
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age = 20
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has_ID = True
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if age >= 18 and has_ID:
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print("Allowed entry.")
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else:
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print("Entry not allowed.")
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```
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Here, both `age >= 18` and `has_ID` must be true for entry to be allowed.
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- **Example 2:**
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```python
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has_ticket = False
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vip_pass = True
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if has_ticket or vip_pass:
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print("Entry granted.")
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else:
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print("Entry denied.")
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```
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This example allows entry if the user has either a ticket or a VIP pass.
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- **Example 3:**
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```python
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is_member = False
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if not is_member:
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print("Please sign up to become a member.")
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```
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The `not` operator inverts `is_member`. If `is_member` is `False`, the message is shown.
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---
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## Ternary Expressions
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A ternary expression is a shorthand way to write an `if-else` statement in a single line. It’s useful for simple conditions and assignments.
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**Syntax:**
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```python
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value_if_true if condition else value_if_false
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```
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**Example:**
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```python
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age = 17
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status = "Adult" if age >= 18 else "Minor"
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print(status) # Output: Minor
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```
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Here, `status` is assigned "Adult" if `age >= 18` is true; otherwise, it’s assigned "Minor". Ternary expressions are concise and useful when assigning values based on conditions.
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**Another Example:**
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```python
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is_even = "Even" if num % 2 == 0 else "Odd"
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```
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This checks if a number is even or odd, assigning the appropriate string based on the condition `num % 2 == 0`.

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