使用PHP在数组中交替大写字母

Question

I have an alphanumeric string like below,

$string_1 = "a4nas60dj71wiena15sdl1131kg12b"

and would like to change it to something like below,

$string_2 = "a4NaS60dJ71wIeNa15Sdl1131Kg12B"

How would I go about doing this? I have tried the below code, but it doesn't work.

$lenght = strlen($string_1);

for ( $i = 0; $i <= $length - 1; $i += 1) {

    if ( $i % 2) {

        $string_2[$i]=strtoupper($string_1[$i]);

    }

    else {

        $string_2[$i]=$string_1[$i];

    }

}

echo $string_2;

The above code prints out "Array" so something is definitely not working.

Answer 1

By the way, you have a slight error in your capitalized string:

$string_1: a4nas60dj71wiena15sdl1131kg12b
$string_2: a4NaS60dJ71wIeNa15Sdl1131Kg12B
                               ^ should be capital so out of sync for rest of string

I'll give you two ways of doing it:

<?php
header('Content-Type: text/plain');

$string_1 = "a4nas60dj71wiena15sdl1131kg12b";
$string_2 = "a4NaS60dJ71wIeNa15Sdl1131Kg12B";

$letter_count = 0;
$result = '';
for ($i=0; $i<strlen($string_1); $i++) {
    if (!preg_match('![a-zA-Z]!', $string_1[$i])) {
        $result .= $string_1[$i];
    } else if ($letter_count++ & 1) {
        $result .= strtoupper($string_1[$i]);
    } else {
        $result .= $string_1[$i];
    }
}

$result2 = preg_replace_callback('!([a-zA-Z]\d*)([a-zA-Z])!', 'convert_to_upper', $string_1);

function convert_to_upper($matches) {
    return strtolower($matches[1]) . strtoupper($matches[2]);
}

echo "$string_1
";
echo "$string_2
";
echo "$result
";
echo "$result2
";
?>

Note: The above makes several assumptions:

1. Characters other than numbers and letters can be in the string;
2. You want to alternate case regardless of the original (eg "ASDF" becomes "aSdF");
3. You're capitalizing every second letter, not every second lowercase letter.

The above can be altered if these assumptions are incorrect.