PHP: Conditional constructions (if)

Logical expressions let you check different conditions. But on their own, they only return true or false. So that a program can perform different actions depending on the result, PHP has a special if construct:

<?php

if (5 > 3) {
    print_r('Yes, it is true');
}

Here the string 'Yes, it is true' is printed, because the condition 5 > 3 is true.

┌───────────┐
│ condition?│
└─────┬─────┘
 true │
      ↓
┌───────────┐
│ if body   │
└───────────┘

Code blocks

After the word if, the condition is written in parentheses, and then a block of code is described in curly brackets. All the instructions inside the curly brackets belong to a single block:

<?php

if (10 === 10) {
    print_r("First\n");
    print_r("Second\n");
}

print_r('Goodbye!');

Here First and Second are printed, because the condition was satisfied. And Goodbye! is printed in any case, since this instruction is already outside the block. The principle is the same as in function definitions.

Using if inside a function

Let's look at a function that determines the type of a sentence passed to it. If it ends with a question mark, the function returns 'question', otherwise it returns 'normal':

<?php

function getTypeOfSentence(string $sentence): string
{
    // A simple way to extract the last character
    $lastChar = $sentence[-1];

    if ($lastChar === '?') {
        return 'question';
    }

    return 'normal';
}

print_r(getTypeOfSentence('Hodor') . "\n");  // => normal
print_r(getTypeOfSentence('Hodor?') . "\n"); // => question

Here two return statements are used at once. If the condition inside if is satisfied, return 'question'; fires and the function ends. If the condition isn't satisfied, control passes to the next line with return 'normal';.

So the function has several possible exit points. This is a common practice. Depending on the conditions, the function can end in different ways.

Even though the getTypeOfSentence() function uses if, it returns strings, which means it isn't a predicate. As a predicate, let's look at a function that checks whether there's enough money for a purchase:

<?php

function hasEnoughMoney(int $balance, int $price): bool
{
    if ($balance >= $price) {
        return true;
    }

    return false;
}

var_dump(hasEnoughMoney(100, 50)); // => bool(true)
var_dump(hasEnoughMoney(30, 50));  // => bool(false)

if and logical expressions

We wrote the hasEnoughMoney() function using if. But in this form it could do without it, because the result of the comparison is itself already a logical expression:

<?php

function hasEnoughMoney(int $balance, int $price): bool
{
    return $balance >= $price;
}

In simple cases, it's better to return such an expression right away. if is needed where additional actions are performed inside the block besides returning the result. The more complex the programs we write, the more often such situations will come up.

In a quiz, the number 42 is the secret answer. A player names a number, and the program tells them right away whether they guessed it or not. Implement a function guessNumber() that takes a number and checks whether it's equal to 42. If it's equal, it returns 'You win!', otherwise 'Try again!'.

<?php

guessNumber(42); // 'You win!'
guessNumber(61); // 'Try again!'