How PHP code simplifies

How to simplify PHP code
How to simplify the following code to return only once {"status": 0, "Error_code": 0} ' means two 0 is the variable has a problem and return that code. Code implementation
Public Function login () {

$a _id =$_get[' a_id '];
$a _password=$_get[' A_password '];

if (empty ($a _id)) {
$this->error (' user name cannot be null ');
echo ' User ID cannot be empty {' status ': 0, ' Error_code ': 101} ';
Exit
}
if (empty ($a _password)) {
$this->error (' password cannot be null ');
echo ' password cannot be empty {' status ': 0, ' Error_code ': 101} ';
Exit
}
$password = MD5 ($password);

$admin = M (' admin ');
$where = "a_id= ' $a _id ' and a_password= ' $a _password '";
$count = $admin->where ($where)->count ();
$row = $admin->where ($where)->find ();
Var_dump ($row); exit;
if ($row [' a_id ']) {
Session (' a_id ', $row [' $a _id ']);
Echo ' {' status ': 1, ' Error_code ': 100} ';
Exit
} else {
$this->error (' User name or password is wrong, please re-login ');
echo "Login failed! ";
Echo ' {' status ': 0, ' Error_code ': 104} ';
Exit
}
}
------to solve the idea----------------------

Public Function login () {
  $res = Array (' status ' = = 0, ' error_code ' = ' + ', ' msg ' = = ');
  $a _id =$_get[' a_id '];
  $a _password=$_get[' A_password '];
  while (1) {
    if (empty ($a _id)) {
      $res [' error_code '] = 101;
      $res [' msg ' = ' user name cannot be empty ';
      Break
    }
    if (empty ($a _password)) {
      $res [' error_code '] = 101;
      $res [' msg ' = ' password cannot be null ';
      Break
    }
    $admin = M (' admin ');
    $where = "a_id= ' $a _id ' and a_password= ' $a _password '";
    $row = $admin->where ($where)->find ();
    if ($row [' a_id ']) {
      Session (' a_id ', $row [' $a _id ']);
      $res [' Status ' = 1;
      Break
    }
    $res [' error_code '] = 104;
    $res [' msg '] = ' username or password error, please re-login ';
    Break
  }
  echo JSON ($res);
}

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