Control structures in PHP enable developers to implement decision-making and repetitive tasks. This lesson covers conditional statements (if-else, switch-case) and loops (for, while, do-while, foreach) in detail, with examples and use cases.
5.1 If-Else Statements
What is an If-Else Statement?
- If-else statements execute a block of code based on a condition.
- Syntax:
if (condition) {
// Code to execute if condition is true
} elseif (another_condition) {
// Code to execute if another_condition is true
} else {
// Code to execute if no condition is true
}Example: Simple If-Else
$age = 20;
if ($age >= 18) {
echo "You are eligible to vote.";
} else {
echo "You are not eligible to vote.";
}
Example: If-Elseif-Else
$score = 85;
if ($score >= 90) {
echo "Grade: A";
} elseif ($score >= 75) {
echo "Grade: B";
} else {
echo "Grade: C";
}
5.2 Switch-Case Statements
What is a Switch-Case Statement?
- A switch-case statement evaluates a variable against multiple possible values and executes corresponding code.
- Syntax:
switch (variable) {
case value1:
// Code to execute if variable equals value1
break;
case value2:
// Code to execute if variable equals value2
break;
default:
// Code to execute if no case matches
}Example: Switch-Case
$day = "Tuesday";
switch ($day) {
case "Monday":
echo "Start of the work week!";
break;
case "Friday":
echo "Almost weekend!";
break;
case "Saturday":
case "Sunday":
echo "It's the weekend!";
break;
default:
echo "Just another weekday.";
}
5.3 Loops
Why Use Loops?
Loops allow repetitive execution of code blocks as long as a specified condition is met.
5.3.1 For Loop
Syntax
for (initialization; condition; increment/decrement) {
// Code to execute
}Example: Print Numbers
for ($i = 1; $i <= 5; $i++) {
echo "Number: $i
";
}Example: Multiplication Table
for ($i = 1; $i <= 10; $i++) {
echo "5 x $i = " . (5 * $i) . "
";
}5.3.2 While Loop
Syntax
while (condition) {
// Code to execute
}Example: Print Even Numbers
$num = 2;
while ($num <= 10) {
echo "Even Number: $num
";
$num += 2;
}
Example: Factorial Calculation
$n = 5;
$factorial = 1;
while ($n > 0) {
$factorial *= $n;
$n--;
}
echo "Factorial: $factorial";
5.3.3 Do-While Loop
Syntax
do {
// Code to execute
} while (condition);Example: Print Numbers
$num = 1;
do {
echo "Number: $num
";
$num++;
} while ($num <= 5);
Difference Between While and Do-While
- In a while loop, the condition is checked before the first iteration.
- In a do-while loop, the code executes at least once, even if the condition is false.
5.3.4 Foreach Loop
Purpose
- Designed specifically for iterating over arrays.
Syntax
foreach ($array as $value) {
// Code to execute
}Example: Iterate Over Array
$fruits = array("Apple", "Banana", "Cherry");
foreach ($fruits as $fruit) {
echo "Fruit: $fruit
";
}
Example: Key-Value Pairs
$person = array("Name" => "Alice", "Age" => 25, "City" => "New York");
foreach ($person as $key => $value) {
echo "$key: $value
";
}
Activities and Exercises
- If-Else Statement:
- Write a script to determine whether a given year is a leap year or not.
- Switch-Case Statement:
- Create a script that takes a number (1–7) and outputs the corresponding day of the week.
- Loops:
- Use a for loop to print the first 10 Fibonacci numbers.
- Write a while loop that prints all odd numbers between 1 and 20.
- Use a foreach loop to display all items in an associative array of student names and grades.
Assignment
Create a PHP script that:
- Uses an if-else statement to check whether a number is positive, negative, or zero.
- Uses a switch-case statement to output the month name when given a number (1–12).
- Uses a for loop to calculate the sum of numbers from 1 to 100.
- Uses a while loop to find the largest power of 2 less than a given number.
- Uses a foreach loop to display a list of products with their prices.
Summary
Control structures are crucial in PHP for decision-making and iteration. The concepts covered in this lesson form the backbone of logical programming in PHP and will be extensively used in real-world applications. Let me know if you'd like additional examples or exercises!
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