Detect if a string contains any numbers

Question

This is the test.php file:

$string = 'A string with no numbers';

for ($i = 0; $i <= strlen($string)-1; $i++) {
    $char = $string[$i];
    $message_keyword = in_array($char, range(0,9)) ? 'includes' : 'desn\'t include';
}

// output
echo sprintf('This variable %s number(s)', codeStyle($message_keyword));

// function
function codeStyle($string) {
    return '<span style="background-color: #eee; font-weight: bold;">' . $string . '</span>';
}

It splits the string character by character and checks if the character is a number or not.

Problem: Its output is always "This variable includes number(s)". Please help me to find the reason. TIP: When I change range(0,9) to range(1,9) It works correctly (But it can't detect 0).

you are always resetting `$message_keyword` on each loop, by the time you get to checking it it is the value of the last loop — Patrick Evans, Sep 08 '13 at 12:07
@Patrick Evans: Yes, You're right. But the last character is not a number. Why does it return "includes"? — Programmer.zip, Sep 08 '13 at 12:17
take a look at the answers below, particularly hek2mgl and dec-null-dweller's, they explain about php's type comparisons — Patrick Evans, Sep 08 '13 at 12:33

hek2mgl · Accepted Answer · 2013-09-08T12:40:33.450

43

Use preg_match():

if (preg_match('~[0-9]+~', $string)) {
    echo 'string with numbers';
}

Althought you should not use it, as it is much slower than preg_match() I will explain why your original code is not working:

A non numerical character in the string when compared to a number (in_array() does that internally) would be evaluated as 0 what is a number. Check this example:

var_dump('A' == 0); // -> bool(true)
var_dump(in_array('A', array(0)); // -> bool(true)

Correct would be to use is_numeric() here:

$keyword = 'doesn\'t include';
for ($i = 0; $i <= strlen($string)-1; $i++) {
    if(is_numeric($string[$i]))  {
       $keyword = 'includes';
       break;
    }
}

Or use the string representations of the numbers:

$keyword = 'doesn\'t include';
// the numbers as stings
$numbers = array('0', '1', '2', /* ..., */ '9');

for ($i = 0; $i <= strlen($string)-1; $i++) {
    if(in_array($string[$i], $numbers)){
       $keyword = 'includes';
       break;
    }
}

edited Sep 08 '13 at 12:40

answered Sep 08 '13 at 12:10

hek2mgl

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Are both `is_numeric()` and `in_array()` are slower than `preg_match()` in this case? – Programmer.zip Sep 08 '13 at 12:58
1

Yeah the problem is the loop that iterates over each char. – hek2mgl Sep 08 '13 at 12:59
would it not work if you used === instead of == in your example? EDIT: lol did not see this is from 2013. was there === already in 2013? – clockw0rk Dec 02 '22 at 10:32
Yes, `var_dump('A'===0)` will produce `bool(false)` but the original question was about `in_array()` – hek2mgl Dec 07 '22 at 20:36
Why not `preg_match('~\d~', $string)` instead of `preg_match('~[0-9]+~', $string)`? – Rodrigo Feb 02 '23 at 20:58

score 12 · Answer 2 · answered Sep 08 '13 at 12:09

12

You can just use regexp :

$message_keyword = preg_match('/\d/', $string) ? 'includes' : 'desn\'t include';

answered Sep 08 '13 at 12:09

OneOfOne

95,033
20
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185

score 3 · Answer 3 · answered Feb 11 '22 at 12:26

3

It's kinda late to answer this question after about 9 years, but If you want to detect integers (and not floats) nothing is better than ctype_digit. Using this function to detect floats with decimal point or other types would results in returning false.

<?php
$number = "123";
$notNumber = "123abc";
var_dump(ctype_digit($number));
var_dump(ctype_digit($notNumber));
?>

Output

bool(true)
bool(false)

answered Feb 11 '22 at 12:26

TheFaultInOurStars

3,464
1
8
29

2

This doesn't really answer the question, though. `ctype_digit()` only returns true if *every* character is numeric, not if the string *contains* a numeric character. https://www.php.net/manual/en/function.ctype-digit.php – benJ Mar 05 '22 at 08:27

score 2 · Answer 4 · answered Sep 08 '13 at 12:18

2

Better way is using regular expression

<?php
    if (preg_match('#[0-9]#',$string)){
        $message_keyword = 'includes';
    }
    else{
        $message_keyword = 'desn\'t include';
    }  
?>

answered Sep 08 '13 at 12:18

Emil Kaczyński

34
2

score 2 · Answer 5 · answered Sep 08 '13 at 12:23

This is because of PHP loose type comparison, you are comparing string with integer, so PHP internally will cast this string to integer, and all character in your string will be casted to 0.

First step to fix your code, will be to create an array of strings instead of integers:

$numbers = array_map(function($n){ return (string)$n; }, range(0,9));
for ($i = 0; $i <= strlen($string)-1; $i++) {
    $char = $string[$i];
    $message_keyword = in_array($char,$numbers)?'includes' : 'doesn\'t include';
}

This will fix your case, but will not work as you expect it to, since $message_keyword is overwritten on each loop, so will receive message for last character only. If you are aiming to only check if string contains number, you can stop checking after encountering first number:

$message_keyword = 'doesn\'t include';
for ($i = 0; $i <= strlen($string)-1; $i++) {
    $char = $string[$i];
    if(in_array($char, $numbers)) {
        $message_keyword = 'includes';
        break; //found, no need to check next
    }   
}

To have this all logic in more compact form, use regular expresion, as posted by others before.

Nice and clear! What does this mean exactly? `$numbers = array_map(function($n){ return (string)$n; }, range(0,9));` — Programmer.zip, Sep 08 '13 at 12:43
This takes array of integers created by `range` and casts every element to string, so you have an array of string to compare against. — dev-null-dweller, Sep 08 '13 at 12:59

score 0 · Answer 6 · answered Sep 08 '13 at 12:10

array range ( mixed $start , mixed $end [, number $step = 1 ] )

If a step value is given, it will be used as the increment between elements in the sequence. step should be given as a positive number. If not specified, step will default to 1.

In your case, you havent mentioned the third parameter that is why it is always set to 1

See Manual here

Detect if a string contains any numbers

6 Answers6

Output