Getting button value on click and echo it - php

Question

i am a beginner in php and my first task is to build a calculator and I am here to ask how to get a value from a button and just echo it on the same page. I am trying through method post using isset but enable to display any value on the same page.
<form action="" method="POST">
<input type="button" value="0" name="zero">
</form>
<?php
if (isset($_POST["zero"]))
{
echo $_POST["zero"];
}
?>

Answer 1

Only an input[type=submit] will submit the form onclick. It is valid to have multiple submit buttons:
<form action="" method="POST">
<input type="submit" value="0" name="mybutton">
<input type="submit" value="1" name="mybutton">
<input type="submit" value="2" name="mybutton">
</form>
<?php
if (isset($_POST["mybutton"]))
{
echo $_POST["mybutton"];
}
?>
If you want to use input[type=button] then you will need some Javascript to trigger the submit, and a hidden input to transport the value.
<script>
window.onload = function(){
document.getElementsByName("mybutton").onclick = function(){
document.getElementsByName("postvar")[0].value = this.value;
document.forms.myform.submit();
}
};
</script>
<form name="myform" action="" method="POST">
<input type="hidden" name="postvar" value="" />
<input type="button" value="0" name="mybutton">
<input type="button" value="1" name="mybutton">
<input type="button" value="2" name="mybutton">
</form>
<?php
if (isset($_POST["postvar"]))
{
echo $_POST["postvar"];
}
?>

Answer 2

Change
<input type="button" value="0" name="zero">
To
<input type="submit" value="0" name="zero" />
Add an event handler if you want to do it via button click.

Answer 3

Try this
<form action="" method="POST">
<input type="submit" value="0" name="zero">
</form>
<?php
if (isset($_POST["zero"]))
{
echo $_POST["zero"];
}
?>

Answer 4

Use
<input type="submit" value="0" name="zero">
else if you want to use button use javascript
<form action="" method="POST">
<input type="button" value="0" name="zero">
</form>
<script type="text/javascript">
$("input[type='button']").click(function(){
alert(this.value);
});
</script>