What are the recursion rules for PHP functions?

Rules for creating recursive functions in PHP: Define recursive situations: Clarify the conditions for recursive function calls. Provides the base case: the condition under which the function should not be called recursively. Decrease recursion depth: Reduce the nesting level with each recursive call to avoid infinite recursion.

Recursion rules for PHP functions

Recursion is the technique of a function calling itself within itself. In PHP, you can create recursive functions using the following rules:

1. Clearly define recursive situations

The first principle of recursive functions is to clearly define when to call recursively . This means identifying the specific conditions under which a function needs to be recursive in order to perform its task.

2. Provide a base case

The second principle of recursive functions is to provide a base case. This is the condition under which the function should not be called recursively. It allows functions to exit recursive procedures.

3. Decrease recursion depth

Each recursive call will increase the nesting level. If a function does not have a well-defined termination condition, it will recurse infinitely, eventually leading to a stack overflow error. Therefore, it is important to decrease the recursion depth so that the function eventually reaches the base case and exits.

Practical case

The following is a practical case demonstrating PHP recursive function:

<?php

function factorial($num) {
  if ($num == 1) {
    return 1;
  } else {
    return $num * factorial($num - 1);
  }
}

echo factorial(5);  // 输出: 120

?>

Explanation:

This function calculates the factorial of a given number. It uses recursion to keep calling itself, passing the decremented value down. When the number reaches 1, the function returns 1 (base case). Otherwise, it multiplies the number by the result of the recursive call. This recursive process continues until the base case is reached and the final result is returned.

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