# PHP BASICS

[PHP Crash Course](https://www.youtube.com/watch?v=BUCiSSyIGGU)\
[PHP Code Structure Reference Repo](https://github.com/bradtraversy/php-crash/tree/main)

### **Basic PHP Syntax**

#### 1. **PHP Tags**

PHP code is enclosed within `<?php` and `?>` tags.

```php
<?php
// PHP code goes here
?>
```

#### 2. **Comments**

* Single-line comments: `//` or `#`
* Multi-line comments: `/* ... */`

```php
<?php
// This is a single-line comment
# This is also a single-line comment

/*
This is a
multi-line comment
*/
?>
```

#### 3. **Variables**

* Variables start with a `$` sign.
* Variable names are case-sensitive.
* No need to declare variable types (PHP is loosely typed).

```php
<?php
$name = "John";
$age = 25;
?>
```

#### 4. **Echo/Print**

* `echo` and `print` are used to output data.

```php
<?php
echo "Hello, World!";
print "Hello, World!";
?>
```

#### 5. **Data Types**

PHP supports:

* Strings (`"Hello"`)
* Integers (`10`)
* Floats (`3.14`)
* Booleans (`true` or `false`)
* Arrays (`[1, 2, 3]`)
* Objects
* NULL

```php
<?php
$string = "Hello";
$int = 42;
$float = 3.14;
$bool = true;
$array = [1, 2, 3];
$null = null;
?>
```

#### 6. **Concatenation**

Use `.` to concatenate strings.

```php
<?php
$name = "John";
echo "Hello, " . $name;
?>
```

#### 7. **Conditionals**

* `if`, `else`, `elseif`

```php
<?php
$age = 18;
if ($age >= 18) {
    echo "You are an adult.";
} else {
    echo "You are a minor.";
}
?>
```

#### 8. **Loops**

* `for`, `while`, `foreach`

```php
<?php
// For loop
for ($i = 0; $i < 5; $i++) {
    echo $i;
}

// While loop
$i = 0;
while ($i < 5) {
    echo $i;
    $i++;
}

// Foreach loop (for arrays)
$colors = ["red", "green", "blue"];
foreach ($colors as $color) {
    echo $color;
}
?>
```

#### 9. **Functions**

* Define functions using `function`.

```php
<?php
function greet($name) {
    return "Hello, " . $name;
}
echo greet("John");
?>
```

***

### **Most Used PHP Methods**

#### 1. **String Functions**

* `strlen()`: Get string length.
* `str_replace()`: Replace text in a string.
* `strpos()`: Find the position of a substring.
* `substr()`: Get a portion of a string.
* `strtolower()` / `strtoupper()`: Convert to lowercase/uppercase.

```php
<?php
$text = "Hello, World!";
echo strlen($text); // 13
echo str_replace("World", "PHP", $text); // Hello, PHP!
echo strpos($text, "World"); // 7
echo substr($text, 0, 5); // Hello
echo strtolower($text); // hello, world!
?>
```

#### 2. **Array Functions**

* `count()`: Get the number of elements in an array.
* `array_push()`: Add an element to the end of an array.
* `array_pop()`: Remove the last element of an array.
* `array_merge()`: Merge two or more arrays.
* `in_array()`: Check if a value exists in an array.

```php
<?php
$fruits = ["apple", "banana"];
echo count($fruits); // 2
array_push($fruits, "orange");
print_r($fruits); // ["apple", "banana", "orange"]
echo in_array("banana", $fruits); // true
?>
```

#### 3. **File Handling**

* `file_get_contents()`: Read a file into a string.
* `file_put_contents()`: Write data to a file.
* `fopen()`, `fread()`, `fwrite()`, `fclose()`: Advanced file handling.

```php
<?php
$fileContent = file_get_contents("example.txt");
file_put_contents("example.txt", "New content");
?>
```

#### 4. **Superglobals**

* `$_GET`: Data from URL parameters.
* `$_POST`: Data from form submissions.
* `$_SESSION`: Session variables.
* `$_COOKIE`: Cookies.
* `$_SERVER`: Server and execution environment information.

```php
<?php
// Example: Get data from a form
$username = $_POST['username'];
?>
```

#### 5. **Date and Time**

* `date()`: Format a date/time string.
* `time()`: Get the current Unix timestamp.

```php
<?php
echo date("Y-m-d H:i:s"); // 2023-10-05 12:34:56
echo time(); // Current timestamp
?>
```

#### 6. **Database Interaction (MySQLi)**

* `mysqli_connect()`: Connect to a MySQL database.
* `mysqli_query()`: Execute a query.
* `mysqli_fetch_assoc()`: Fetch a result row as an associative array.

```php
<?php
$conn = mysqli_connect("localhost", "user", "password", "database");
$result = mysqli_query($conn, "SELECT * FROM users");
while ($row = mysqli_fetch_assoc($result)) {
    echo $row['username'];
}
mysqli_close($conn);
?>
```

### &#x20;


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