Introduction

When writing a PHP program, we often need to make decisions or repeat certain tasks. For example, checking whether a user can log in, deciding whether a student is pass or fail, printing numbers from 1 to 100, or displaying products in an online store.

This is where Control Flow comes into play. Control Flow decides the order in which PHP code runs. It allows PHP programs to make decisions, choose different paths, and repeat code when required.

What is Control Flow?

Control Flow is the mechanism that controls the execution of a program based on conditions and loops.

Control Flow has two major categories:

1. Decision Making Statements
   • if
   • if...else
   • if...elseif...else
   • switch
2. Looping Statements
   • for
   • while
   • do...while
   • foreach

1. The if Statement

The if statement executes a block of code only when a specified condition is true.

Syntax

if(condition){
    // code
}

Example

<?php

$age = 20;

if($age >= 18){
    echo "Eligible to Vote";
}

?>

Output

Eligible to Vote

2. The if...else Statement

The if...else statement is used when there are two possible outcomes. If the condition is true, the if block runs. Otherwise, the else block runs.

<?php

$marks = 35;

if($marks >= 40){
    echo "Pass";
}else{
    echo "Fail";
}

?>

3. The if...elseif...else Statement

When multiple conditions need to be checked, we use if...elseif...else. It is useful when a program has more than two possible results.

<?php

$score = 82;

if($score >= 90){
    echo "Grade A+";
}
elseif($score >= 75){
    echo "Grade A";
}
elseif($score >= 60){
    echo "Grade B";
}
else{
    echo "Grade C";
}

?>

4. The switch Statement

The switch statement compares one variable with multiple possible values. It is cleaner than writing many if...elseif conditions.

<?php

$day = "Sunday";

switch($day){

    case "Sunday":
        echo "Holiday";
        break;

    case "Monday":
        echo "Working Day";
        break;

    default:
        echo "Normal Day";
}

?>

5. The for Loop

A for loop is used when the number of repetitions is already known. It is commonly used for counting and fixed repeated tasks.

<?php

for($i = 1; $i <= 5; $i++){
    echo $i . "<br>";
}

?>

Output

1
2
3
4
5

6. The while Loop

The while loop continues executing as long as the condition remains true. It is useful when we do not know exactly how many times the loop will run.

<?php

$i = 1;

while($i <= 5){
    echo $i . "<br>";
    $i++;
}

?>

7. The do...while Loop

The do...while loop executes the code block first and checks the condition afterward. This means the loop runs at least once.

<?php

$i = 1;

do{
    echo $i . "<br>";
    $i++;
}
while($i <= 5);

?>

8. The foreach Loop

The foreach loop is specially designed for arrays. It automatically visits every element without using an index.

<?php

$fruits = ["Apple", "Banana", "Mango"];

foreach($fruits as $fruit){
    echo $fruit . "<br>";
}

?>

Comparison of All Statements

Statement	Purpose	Best Use Case
if	Check one condition	Login validation
if...else	Two possible outcomes	Pass/Fail
if...elseif...else	Multiple conditions	Grading system
switch	Match one value against many cases	Menus and navigation
for	Known number of repetitions	Tables and counters
while	Repeat while condition is true	Downloads and queues
do...while	Execute at least once	ATM menus
foreach	Traverse arrays	Product or user lists

Practical Scenario: Online Shopping Website

Suppose you are building an online shopping website:

• if → Check whether the user is logged in.
• if...else → Determine if payment succeeded or failed.
• if...elseif...else → Apply discounts based on order value.
• switch → Choose payment method such as UPI, Card, or COD.
• for → Generate invoice line numbers.
• while → Process pending orders until none remain.
• do...while → Keep asking for coupon codes until the user exits.
• foreach → Display all products in the shopping cart.

Practice Questions

1. Write a program to check whether a number is positive or negative using if...else.
2. Create a grading system using if...elseif...else.
3. Display the weekday name using a switch statement.
4. Print numbers from 1 to 20 using a for loop.
5. Print even numbers between 2 and 50 using a for loop.
6. Use a while loop to print numbers from 10 to 1.
7. Write a do...while loop that prints numbers from 1 to 5.
8. Create an array of five programming languages and print them using foreach.
9. Print the multiplication table of 8 using a for loop.
10. Calculate the sum of numbers from 1 to 100 using any loop.

Mini Quiz

Conclusion

Control Flow is the backbone of PHP programming. It enables applications to make decisions, repeat tasks, and process data efficiently. Whether you are building a login system, an online shopping platform, a student portal, or a banking application, you will use if, switch, and loops extensively.

By mastering these concepts and practicing real-world examples, you will be ready to build dynamic PHP applications and answer interview questions with confidence.