The difference between intval and int in data type conversion in php

intval("A")=0;
intval(12.3223)=12;
intval("1123Asdfka3243")=1123;
< p>$a=0.99;
$b=(int)$a; //$b=0;
$a=1.99;
$b=(int)$a; / /$b=1;