# Control Structures

Control structures are used to **control the flow** of execution in a program. They help your code make decisions, repeat tasks, and react to different situations.

In Python, the main types of control structures are:

1. **Conditional Statements** (`if`, `elif`, `else`)
2. **Match-Case** (introduced in Python `3.10`)
3. **Loops** (`for`, `while`)
4. **Loop Control Statements** (`break`, `continue`, `pass`)

## Conditional Statements

Conditional statements allow your program to decide what to do based on certain conditions.

Syntax:

```python
if condition:
    # code runs if condition is True
elif another_condition:
    # runs if the first was False and this is True
else:
    # runs if none of the above are True
```

Example:

```python
x = 5

if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")

# Output: Positive
```

{% hint style="info" %}
You can use `if` without using `elif` and `else` as well. Even just `if-else`.
{% endhint %}

Example:

```python
x = 5

if x > 0:
    print("Positive")

# Output: Positive
```

## Match-Case

`match-case` is similar to `switch-case` in other languages. It's used to match a value against different patterns.

Syntax:

```python
match variable:
    case value1:
        # do something
    case value2:
        # do something else
    case _:
        # default case (like "else")
```

Example:

```python
fruit = "apple"

match fruit:
    case "apple":
        print("Its an apple")
    case "banana":
        print("Its a banana")
    case _: # Here '_' is for default. If nothing matches, this gets matched.
        print("Unknown fruit")

# Output: It’s an apple
```

## Loops

Loops are used to repeat a block of code multiple times.

### For Loop

Used to iterate over sequences like lists, strings, or ranges.

Example:

```python
for i in range(3):
    print(i)

# Output:
# 0
# 1
# 2
```

#### Looping through a list

We also call it *iterating through a list*.

<pre class="language-python"><code class="lang-python">fruits = ["apple", "banana", "cherry"]
<strong># Note: We can iterate over any data types we learned so far and not just lists.
</strong>
for i in fruits:
    print(i)

# Output:
# apple
# banana
# cherry
</code></pre>

### While Loop

Repeats as long as a condition is `True`.

```python
x = 0

while x < 3:
    print(x)
    x += 1

# Output:
# 0
# 1
# 2
```

## Loop Control Statements

These help manage how loops behave.

### break

Exits the loop immediately.

```python
for i in range(5):
    if i == 3:
        break
    print(i)

# Output:
# 0
# 1
# 2
```

### continue

Skips the current iteration and moves to the next.

```python
for i in range(5):
    if i == 2:
        continue
    print(i)

# Output:
# 0
# 1
# 3
# 4
```

### pass

Used as a placeholder. Does nothing, just a syntactic placeholder.

```
for i in range(3):
    pass  # this loop does nothing
```

## Nested Control Structures

You can use control structures inside each other.

```python
for i in range(3):
    if i % 2 == 0:
        print(f"{i} is even")
    else:
        print(f"{i} is odd")

# Output:
# 0 is even
# 1 is odd
# 2 is even
```

{% hint style="info" %}
We can create nested control structures as much as we like, just like we learned with [Variables and Data Types](/fundamentals/python/basics-of-python/variables-and-data-types.md).
{% endhint %}

## The `else` clause with loops

Yes, Python allows `else` to be used with loops!

* In a `for` or `while` loop, the `else` block runs if the loop **didn’t break**.

```python
for i in range(5):
    print(i)
else:
    print("Loop finished normally")

# Output:
# 0
# 1
# 2
# 3
# 4
# Loop finished normally
```

If a `break` happens, the `else` part is skipped.

```python
for i in range(5):
    if i == 3:
        break
    print(i)
else:
    print("Loop finished normally")

# Output:
# 0
# 1
# 2
```


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