Errors are the unwanted conditions which interrupts the normal flow of the program.

Errors can be categorized in two :

Syntax Error : If there is any symbol missing or mistake in the statements of the program those are syntax errors.

Logical Error : If there is any logical mistakes like divide by zero then those errors are termed as logical errors.

In PHP there are 3 types of errors :

1) notice error
2) warning
3) Fetal

1) notice error

The notice error occurred when a variable is not declared and it is been used at some point then the notice error is given. To avoid this error we should use the "@" in place of "$" before variable.

for example:

<?php

for($i=1;$i<=10;$i++)
{
    echo  $i;
}

?>

2) warning

If there is any error and still the output is displayed then the warning is shown. These errors doesn't halt the execution of the program.

<?php
   include('Request.php');
   echo "Hello!";
?>

The warning that will be displayed be like
Output Warning: include(Request.php) [function.include]: failed to open stream: No such file or directory in C:xampplitehtdocs18-06loopsum.php on line 2
Hello

3) Fetal

Fetal errors are the one which terminates the execution of the program if any error occurs. these kind of errors occurs like if you are calling a file through require function and the file doesn't exists or something happens then the require() will terminate the execution and displays the error.