PHP Conditional Statements

Conditional statements are used to execute different code blocks based on different conditions. A conditional evaluates a Boolean expression. If the expression is true, it will execute everything inside its block of code. A block of code is a group of statements enclosed by {}.

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Conditions are True or False

At the core of any decision-making logic is a Boolean expression, or code that is either true or false.

Conditions are expressions that PHP tests or evaluates to see whether they are true or false. To set up conditions, you compare values using comparison operators.

Examples

  • Are two values equal?
  • Is one value larger or smaller than another?
  • Does a string match a pattern? 
  • Does the ZIP code have five numeric characters?
  • Does a variable have any value assigned at all?
  • Does a file or folder exist?
  • Does a variable contain a value of a particular data type?

You can also set up conditions in which you ask two or more questions.

Comparing Values

You can compare numbers or strings to see whether they are equal, whether one is larger than the other, or whether they are not equal. You compare values with comparison operators. PHP evaluates the comparison and returns true or false.

You can compare both numbers and strings. Strings are compared alphabetically, with all uppercase characters coming before any lowercase characters. For example, SS comes before Sa.

Strings are compared based on their ASCII code. In the ASCII character set, each character is assigned an ASCII code that corresponds to a number between 0 and 127. When strings are compared, they are compared based on this code. For example, the number that represents the comma is 44. The period corresponds to 46. Therefore, if a period and a comma are compared, the period is evaluated as larger.

Checking Variable Content

Sometimes you just need to know whether a variable exists or what type of data is in the variable.

isset($varname): True if variable is set, even if nothing is stored in it.

empty($varname): True if value is 0 or is a string with no characters in it or is not set.

You can also test what type of data is in the variable.

  • is_int($number)
  • is_array($var2)
  • is_float($number)
  • is_null($var1)
  • is_numeric($string)
  • is_string($string)

You can test for a negative condition, as well, by using an exclamation point (!) in front of the expression.

Joining Multiple Comparisons

Often you need to ask more than one question to determine your condition. This requires you to join comparisons, which have the following the general format:

comparison1 and|or|xor comparison2 and|or|xor comparison3

Comparisons are connected by one of the following three words:

  1. and: Both comparisons are true.
  2. or: One or both comparisons are true.
  3. xor: Only one of the comparisons is true.

Conditional Statements

A conditional statement executes a block of statements only when certain conditions are true. Two useful types of conditional statements are:

  1. An if statement: Sets up a condition and tests it. If the condition is true, a block of statements is executed.
  2. A switch statement: Sets up a list of alternative conditions. It tests for the true condition and executes the appropriate block of statements.

1. if Statements

A conditional is defined by the keyword if followed by a Boolean expression in parentheses and by a block of code. If the expression is true, it will execute the block, otherwise it will skip it. 

You can increase the power of conditionals by adding the keyword else. This tells PHP to execute some block of code if the previous conditions were not satisfied.

You can also add an elseif keyword followed by another condition and a block of code to continue asking PHP for more conditions. You can add as many elseif conditions as you need after an if. If you add an else, it has to be the last one of the chain of conditions. As soon as PHP finds a condition that resolves to true, it will stop evaluating the rest of conditions.

if (condition)
{
  block of statements
}
elseif (condition)
{
  block of statements
}
else
{
  block of statements
}

Alternative Syntax

PHP has an alternative syntax for the conditional statements. In this syntax, the if statement’s opening bracket is replaced with a colon, the closing bracket is removed, and the last closing bracket is replaced with the endif keyword.

if ($x == 1): echo "x is 1";
elseif ($x == 2): echo "x is 2";
else: echo "x is something else";
endif;

2. switch Statements

A switch statement is a conditional structure that tests a variable against several possible values, or cases. This structure evaluates only one expression, and executes the block depending on its value.

For most situations, the if conditional statement works best. However, sometimes you have a list of conditions and want to execute different statements for each condition.

switch ($variable_name)
{
case value:
  block of statements;
  break;
case value:
  block of statements;
  break;
...
default:
  block of statements;
  break;
}

The switch statement tests the value of $variable_name. The script then skips to the case section for that value and executes statements until it reaches a break statement or the end of the switch statement. If there is no case section for the value of $variable_name, the script executes the default section.

When the case matches the current value of the expression, PHP executes the code inside it. As soon as PHP finds a break statement, it exits the switch…case. In case none of the cases are suitable for the expression, PHP executes the default, if there is one, but that is optional.

The breaks are mandatory if you want to exit the switch…case. If you do not specify any, PHP will keep on executing statements, even if it encounters a new case.

Alternative Syntax

The switch statement also has an alternative syntax, which uses the endswitch keyword to terminate the statement.

switch ($x):
case 1: echo "x is 1"; break;
case 2: echo "x is 2"; break;
default: echo "x is something else";
endswitch;

The alternative syntax is often preferable for longer conditional statements since it then becomes easier to see where those statements end.

3. match Statements

A match statement chooses a value for a variable based on the value of another variable. You could accomplish the same task with a switch statement, but match statements are written much more compactly.

Also, match statements rely on strict comparisons (the equivalent to testing for identity with ===), whereas switch statements make comparisons after any relevant type juggling (the equivalent to testing for equality with ==).

$country = 'Ireland';

$currency = match ($country) {
'UK' => 'pound',
'Ireland' => 'euro',
'France' => 'euro',
'Spain' => 'euro',
'USA' => 'dollar',
default => '(country not recognized)'
};

4. Ternary Operator

In addition to the if and switch statements, there is the ternary operator (?:) or three-part operator. This operator can replace a single if/else clause. The operator takes three expressions. If the first one is evaluated to true, then the second expression is returned, and if it is false, the third one is returned.

Ternary operator expression:

$y = ($x == 1) ? 1 : 2;

In PHP, this operator be used as an expression and as a statement.

Ternary operator statement:

($x == 1) ? $y = 1 : $y = 2;

The programming term expression refers to code that evaluates to a value, whereas a statement is a code segment that ends with a semicolon or a closing curly bracket.

5. Null-Coalescing Operator

Another operator that chooses between two values is the null-coalescing operator, indicated with a double question mark (??). This operator makes its choice depending on whether a variable is NULL.