In PHP, the judgment logic is implemented through if, else and elseif. When using it, you need to pay attention to the structure order and nesting depth. 1. If the condition is met, the corresponding code block will be executed, otherwise it will enter elseif or else; 2. elseif can be used multiple times, but the order affects the judgment result; 3. else is used to deal with all cases that are not matched; 4. Incorrect condition order will cause logical confusion; 5. Avoid multi-layer nesting, you can reduce levels by returning in advance; 6. Simple judgment can use ternary operators to simplify the code. Mastering these key points can improve code clarity and maintainability.
When writing PHP code, judgment logic is the most basic and common requirement. if , else and elseif are the core structures that implement these judgments. If used well, it will make the code clear and easy to understand. If used poorly, it will easily make mistakes or make others unable to understand.
Don't mess with the basic structure
The conditional statements of PHP are mainly three parts: if , else if (can also be written elseif ) and else . The basic logic is: if a certain condition is met, execute a piece of code; otherwise, you can check another condition, or go directly to the default branch.
To give a simple example:
$score = 85;
if ($score >= 90) {
echo "excellent";
} elseif ($score >= 80) {
echo "good";
} else {
echo "General";
}The above code will output "good" because the score is between 80 and 89. This structure is very common, but a few things to note:
-
elseifandelse ifare equivalent, but the writing method is different. - Each condition will only be judged when the previous condition is not true.
-
elseis optional, but plus it can cover all misses.
The order of conditions must be reasonable
When using multiple elseif , the order is important. PHP is judged from top to bottom. As long as one condition is true, you will not look at the following ones again.
For example, the following example:
$age = 17;
if ($age >= 21) {
echo "can drink";
} elseif ($age >= 18) {
echo "can vote";
} else {
echo "Minor";
}What is output here is "minor", because 17 does not meet the first two conditions. But if you change the order of judgment:
if ($age >= 18) {
echo "can vote";
} elseif ($age >= 21) {
echo "can drink";
} Even if $age is 22, it will only output "vote can be voted" because the first condition has been met. So if the order is wrong, the logic may be completely messed up.
Avoid being too deep in nesting
Sometimes we encounter multi-layer judgment situations, such as:
if ($userLoggedIn) {
if ($isAdmin) {
// Show management interface} else {
// Show normal user interface}
} else {
// Prompt login} While this will solve the problem, if you nest too many layers, the code will become difficult to read. At this time, you can consider using return or ending the process early to reduce the level.
For example:
if (!$userLoggedIn) {
echo "Please log in first";
return;
}
if ($isAdmin) {
echo "Welcome Administrator";
return;
}
echo "Welcome to ordinary users";Does this look much more refreshing? The key is to avoid nesting layers and deal with special circumstances first.
Simple judgment can be simplified by ternary operators
Some simple if/else can be replaced by ternary operators to make the code more concise.
for example:
$isMember = true; $message = $isMember ? "Welcome back" : "Please register";
Equivalent to:
if ($isMember) {
$message = "Welcome back";
} else {
$message = "Please register";
} But be careful not to abuse it. It is clearer to use if/else for complex logic.
Basically that's it. If you master the usage of if , else if and else , it will not be difficult to write code that is clear and easy to maintain.
The above is the detailed content of PHP If, Else, and Elseif. For more information, please follow other related articles on the PHP Chinese website!
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