为什么Java和PHP的相同代码不起作用？

Question

I wrote a program in PHP and Java which generates all possible words with length 2. I used recursion. Why does the program work in Java but not in PHP? It's the same code.

Java

package com.company;


public class Words {
public static void main(String[] args) {
    generate("", 2);
}

static void generate(String prefix, int remainder) {
    if (remainder == 0) {
        System.out.println(prefix);
    } else {
        for (char c = 'A'; c <= 'Z'; c++) {
            generate(prefix + c, remainder - 1);
        }
    }
}
}

PHP

generate('', 2);

function generate($prefix, $remainder)
{
if ($remainder == 0) {
    echo "$prefix\n";
} else {
    for ($c = 'A'; $c <= 'Z'; $c++) {
        generate($prefix . $c, $remainder - 1);
    }
}
}

Answer 1

$c has string type in PHP. The ++ operator works differently for it compared to numbers.

PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in PHP and Perl $a = 'Z'; $a++; $a = 'Z'; $a++; turns $a into 'AA' , while in C a = 'Z'; a++; a = 'Z'; a++; turns a into '[' (ASCII value of 'Z' is 90, ASCII value of '[' is 91) . Note that character variables can be incremented but not decremented and even so only plain ASCII alphabets and digits (az, AZ and 0-9) are supported. Incrementing/decrementing other character variables has no effect, the original string is unchanged.

Source: http://php.net/manual/en/language.operators.increment.php

Answer 2

Change your loop from

for ($c = 'A'; $c <= 'Z'; $c++) {

to

foreach (range('A', 'Z') as $c){

============================

EDIT :

Sorry, I tried to find an official document about this, but I cannot. So I'll try to explain a little

In php, when you compare 2 strings, the system wil try to compare the first character and then the second ..... the compare operator will be stop when the first different character appear

Example

$a = 'ABCDEZ';
$b = 'ABCEZZ';

String $b greater than $a because the value ABC in the beginning of $a and $b is the same but E (the value in index 3 of string $b) greater than D (the value in index 3 of string $a), and they don't need to compare other characters

In this question, the original loop is

for ($c = 'A'; $c <= 'Z'; $c++) {

it's fine until $c = 'Z', but after that $c++ will be 'AA' and when php start to compare it, 'AA' < 'Z' and the loop continue, that's why I changed the loop to

foreach (range('A', 'Z') as $c){

To make it work

I hope you enjoy it and happy with my explain, sorry because I don't see any document about this, it's just how php work and I know it