string matching via if statement PHP

Question

I have an input text area which when filled out and sent, puts whatever was typed in into the variable

$input

This is then put through an if statement to check whether or not its the letter a. If it is then echo - you wrote the letter a, else - you did not write the letter a.

<?php    
 $input = $_POST["textarea"];

    echo $input;
    echo "<br />";

    if($input = "a"){
    echo "You wrote a";
    }else{
    echo "You did not write a";
    }


    ?>

It does work, but in the wrong way. Every letter I type in comes as 'You wrote a'. I only want it to echo this if the user typed a. Otherwise, echo 'You did not write a' .

EDIT: When I try == instead of = it says 'You did not write a' for everything. Even when I type a.

EDIT 2: When I try the string compare parameter, It didnt work. Any suggestions where I am going wrong?

FULL SCRIPTS OF BOTH PAGES:

index.php

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

</head>

<body>
<h1>Fun Translator</h1>

<form method="post" action="query.php">
 <textarea name="textarea" id="textarea">
 </textarea>
 <input type="submit" name="send" value="Translate" />
</form>


</body>
</html>

query.php

<?php
$input = $_POST["textarea"];

echo $input;
echo "<br />";

if(strcmp($input,'a')==0){
    echo "You wrote a";
    }else{
    echo "You did not write a";
    }


?>

Solution:

trim()

They all are telling you that you are assigning the letter "a" to the variable $input. To compare the two, you must use ==. Close your eyes and accept an answer :) — horatio
– horatio, Commented Mar 10, 2011 at 18:02
Okay, can you post the full code of the first page, and the second page? Just so's I can try this for myself? — David Thomas
– David Thomas, Commented Mar 10, 2011 at 18:02
Are you really only typing a single a into a textarea? What is it you actually want to compare against - presence of an a at the start of the string maybe? — mario
– mario, Commented Mar 10, 2011 at 18:04

Mark Grey · Accepted Answer · 2011-03-10 18:30:41Z

13

== is the conditional for comparison. = is the assignment operator.

if($input == "a"){
    echo "You wrote a";
    }else{
    echo "You did not write a";
    }

You might want to use strcmp as it is binary-safe.

if(strcmp($input,'a')==0){
    echo "You wrote a";
    }else{
    echo "You did not write a";
    }

http://php.net/manual/en/language.operators.comparison.php

http://php.net/manual/en/function.strcmp.php

EDIT: Taking another stab here - in your code as posted (I copy pasted it) you have whitespace in your textarea by default.

Don't put a line break between the and tags. This adds whitespace to the start of 'a'.

Removing this made it work properly in my test.

EDIT: As per the accepted answer and reposted code, trim() is in fact the proper function to remove all leading and trailing whitespace.

edited Mar 10, 2011 at 18:30

answered Mar 10, 2011 at 17:58

Mark Grey

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5 Comments

Mark Grey Over a year ago

It returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are identical.

Mark Grey Over a year ago

@Ryan Murphy This must be something further down the stack. Can you post the code of your form? Perhaps it's enctype is wrong? Both these comparisons should work if the incoming data is a string and only contains 'a'.

Mark Grey Over a year ago

Thank you for adding the remaining code. Could you run print_r($_POST); in the responding page and post its contents as well?

RSM Over a year ago

it came up with : Array ( [textarea] => a [send] => Translate )

Mark Grey Over a year ago

@Ryan Murphy - Edited for another possible reason - extra whitespace in your textarea tag the 'a' gets appended to. Let me know if this works.

Spudley · Accepted Answer · 2011-03-10 18:14:43Z

Your problem is a confusion between the = and == operators.

If you want to compare two values in PHP, you must use == (that is, two equal signs together).

Using a single equal sign on its own will set the value on the right to the value on the left (as per its use in the first line of your code example).

See this page on the php manual: http://www.php.net/manual/en/language.operators.comparison.php

Note, there is also a tripple-equal operator ===, which is also used for comparison, where you want to also compare the data type of the two sides. For basic use, the double equal is usually sufficient, but the manual page will give you more info on the difference between the two.

[EDIT]

Re your edit - All the comments suggesting == instead of = are right. The single-equal operator is the wrong thing to use. If you're still getting a problem with the double-equal operator, then $input doesn't actually equal a.

In this case, you may need to debug your input. Assuming your echo $input; line does show a, I'd say the most likely scenario is that you're entering some white space with it, maybe a carriage return or something like that.

To prove that, you may want to print it like this:

print "<pre>[".$input."]</pre>";

That will show up any unexpected extra characters you may have entered.

If you're not worried about white space, then use the trim() function to get rid of it.

You could also use functions like strlen() to check how long the string is, etc.

[EDIT AGAIN]

Okay, looking at your HTML code, I'd say it's definitely going to be the white space issue.

<textarea name="textarea" id="textarea">
</textarea>

This will result in the textarea being created with a line feed as it's default content, because the opening and closing <textarea> tags are on separate lines. If you just type a into it, what you'll actually submit will be a plus a line feed.

The best advice is probably to trim() the input before you check it.

dialer · Accepted Answer · 2011-03-10 17:59:17Z

3

Use operator == instead of =

answered Mar 10, 2011 at 17:59

dialer

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1 Comment

dialer Over a year ago

$input = $_POST["textarea"]; // use = here || if($input == "a"){ // use == here

David Thomas · Accepted Answer · 2011-03-10 18:00:19Z

0

= is assignment,

== is comparison.

answered Mar 10, 2011 at 18:00

David Thomas

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1 Comment

David Thomas Over a year ago

@Ryan, I already saw; which is why I asked for the full scripts for both pages in order that I could see what else was going on.

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