如何使用多个正负符号将字符串转换为int？

Question

I'm trying to cast string to int. Everything work fine but have a small problem here

echo (int)"--12"; //return 0, i want 12
echo (int)"---23";//return 0, i want -23
echo (int)"+-99"; //return 0, i want -99
...

Why did this happened and what is the right way to cast in this case? Many thanks!

Answer 1

To evaluate the positive and negative signs so that all positive symbols are ignored and two negatives equal a positive, you can perform a replacement.

Code: (Demo)

$signed_number_strings = ["--1", "---33", "+-444"];

foreach ($signed_number_strings as $string) {
    var_dump((int)preg_replace('~\++|-\+*-\+*~', '', $string));
}

Output:

int(1)
int(-33)
int(-444)

The logic behind the pattern is to first match/remove 1 or more consecutive + signs, OR a - sign followed by zero or more + followed by a - (and absorbing any trailing + signs). If there are any fringe cases that my pattern doesn't correctly handle, please update your question and leave me a comment.

p.s. The extension of my 2nd branch with \+* is an attempt to optimize the pattern so that it doesn't have to restart the pattern. It could have been written as ~\++|-\+*-~ which would be slightly less strain on the eyeballs. (Demo)