Is my php code below sql injection proof? if not how can it be hacked?

[dineshbabu]

$c=mysql_query("select pass from detail where name='$a'");
$d=mysql_fetch_array($c);
if($a=='' || $b=='')
{echo "EMPTY FIELD(S) DECTECTED";
}
else{
if(!strcmp($b,$d[0]))
{
echo "LOGIN SUCCESSFUL";
$_SESSION['log']='yep';
$_SESSION['name']=$a;
header("Location:home.php");
}
else
{ echo "WRONG USERNAME OR PASSWORD";
}
}