how do i clear the screen of a calculator in php - php

Question

i'm trying to find a way to erase the text screen from my calculator when you press the +/- button so it acts more like a real calculator.
i'm pretty new to php (a week or two) so i'm still learning but i cant figure this out.
the php file returns html code where in i have a <input type='text' named result value='$value'>
(calculator screen).
and a series of submit buttons with a name and value of 1,2,3,+,...
when i press a button a char gets added to the string in result.
when i press on the '=' button it reads the string with eval();
and calculates it.
iv'e tried with a function but i cant figure it out some ideas or tips would be very much welcome.
$value = '';
if(isset($_GET['result']))
$value.=$_GET['result'];
if(isset($_GET['1']))
$value .='1';
if(isset($_GET['2']))
$value .='2';
//and so on ...
if(isset($_GET['+']))
$value .='+';
if(isset($_GET['-']))
$value .='-';
if(isset($_GET['='])){
eval('$result = '.$value.';');
$value = $result;}
return "<form action='index.php' method='get'>
<br><input type='text' name='result' value='$value'><br>
<input type='submit' name='1' value='1'>
<input type='submit' name='2' value='2'>
//and so on ...
(the rest of the html code is loaded somewhere else)

Answer 1

This PHP code below will execute JavaScript code to clean the input field,
echo"<script>document.getElementsByName('result')[0].value = '';</script>
This should resolve your question but i have to tell you that PHP isn't suitable choice to make a web calculator, You need to use JavaScript to make a real calculator without refreshing the page.
Please copy this code below to an HTML file and try it so you can get an idea how it works.
First Number
<input type="text" id="firstNumber" value="6" /><br>
Second Number
<input type="text" id="secondNumber" value="5" /><br>
Result
<input type="text" id="result" /><br>
<button type="button" onclick="Calculate();">Calculate</button>
<script>
function Calculate(){
let firstNumber;
let secondNumber;
firstNumber = document.getElementById("firstNumber").value;
secondNumber = document.getElementById("secondNumber").value;
document.getElementById("result").value = Number(firstNumber) + Number(secondNumber);
// "Number" is to tell javascript its a number not a string/text,
// without "Number" it will concat both numbers
}
</script>

Answer 2

You should use brackets for your conditions, especially if you nest them:
if(isset($_GET['result'])) {
$value .= $_GET['result'];
}
And your indentation makes it look like Python, someone reading it would mistake it for a condition nested in another condition and believe that your if(isset($_GET['2'])) is true only if if(isset($_GET['1'])) is also true.
A switch is a better solution here (and even better for the operators since you probably only have four of them), but in any case, you should assign each term of your operation in a single variable.