Bug
A bug is a discrepancy between the expected result of a program and its actual result.
Bugs have many different varieties:
- Code does not compile
- Program stops before completing, with a ‘Fatal error’
- Program outputs a wrong result
- Program outputs a result different from expected
- Program is vulnerable to security attack
- Poor performance.
<?php
// a case of syntax error
// echo hello world;
echo -3 ** 2; // known bug
?>