mysqli\u num\u rows()期望参数1是mysqli\u结果,字符串以C:\wamp\www\DbConnect给出。php在线12

这是我的php代码,每当我运行它时,我都会得到那个错误。。。数据库位于本地主机wamp服务器上

<?php
$username ="root";
$password= "";
$hostname ="localhost";
$database ="mydata";
$check="";
$conn = new mysqli($hostname, $username, $password, $database);
$i = "SELECT * FROM `patient` WHERE 1";
$num_rows = mysqli_num_rows($i);
while($row = mysqli_fetch_array($i))
{
$r[]=$row;
$check=$row["emailid"];
}
if($check==NULL)
{
$r[$num_rows]="Record is not available";
print(json_encode($r));
}
else
{
$r[$num_rows]="success";
print(json_encode($r));
}
//mysql_close($conn);
?>

请对此提出解决方案。