How can one handle undefined variables like "submit" in PHP scripts to avoid errors?

When dealing with undefined variables like "submit" in PHP scripts, it is important to first check if the variable is set using isset() function before using it. This helps to avoid errors that may occur when trying to access a variable that has not been defined. 

if(isset($_POST['submit'])) {
    // Handle form submission
    // Your code here
} else {
    // Display form or error message
}

Keywords

undefined variables error handling isset function empty function strict type checking

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