PHP - 我如何计算数字字符和字符串字符来检查用户名长度值？

how to count numerical character combine with string character in php? if i use strlen, thats only count string. I want limit username input value only 20 character, if i input 20 or more string only, this code work, but if i input (e.g : Admin123Admin123Admin123) thats not work, my validation input fail.

i have a code in yii 2 useraccount controller like this :

        // new user

        if ( $username != '' && $password != '' && intval($group) > 0 && !$exist)
        {
            $myFunctions    = new userFunctions;
            $exist = $myFunctions->isUserNameExist( $username );
            $isValid = $myFunctions->isValidPassword( $password );
            $checkUsername = strlen($username);
            // $temp = str_split($username); // Convert a string to an array by each character
            // // if don't want the spaces
            // $temp = array_filter($temp); // remove empty values
            // $checkUsername = count($temp);

            if ( $isValid == 0 && !$exist)
            {
                $result = $myFunctions->saveNewUser( $username, $password, $group, $expired );
                $error =  ( $result ) ? 0 : 1;
            } 
            else if( $exist )
            {
                $error = 3;
            }
            else $error = 2;
        }
    }

    echo \yii\helpers\Json::encode(['result' => $result, 'error' => $error, 'checkUsername' => $checkUsername ]);

this is my code in view :

                function saveNewUsers()
                {
                    $.ajax({
                                type     :'POST',
                                dataType : 'json',
                                data     : { id: $('#hiUserID').val(), username : $('#txtUsername').val(), password: $('#txtPassword1').val(), group: $('#cbUserGroup').val(), expired: $('#cbExpired').val() },
                                url  : '" . \Yii::$app->getUrlManager()->createAbsoluteUrl('useraccount/saveuser') . "',
                                success  : function(response) {
                                    if ( !response.result ) {
                                        if ( response.error == 2 )
                                        {
                                            $('#errorMessageUser').html(DecodeEntities('{$myLabels[20]}.')).show();
                                        }
                                        else if( response.error == 3 )
                                        {
                                            $('#errorMessageUser').html(DecodeEntities('{$myLabels[56]}.')).show(); 
                                        }
                                        else if( response.checkUsername > 20)
                                        {
                                            $('#errorMessageUser').html(DecodeEntities('{$myLabels[57]}.')).show();     
                                        }
                                        else $('#errorMessageUser').html(DecodeEntities('{$myLabels[22]}.')).show();
                                    }
                                    else {      
                                        $('#errorMessageUser').html('').hide();
                                        $('#myUserModal').modal('hide');
                                        $.pjax.reload({container:'#myPjax',timeout:false});


                                    }   
                                }                       
                    });
                }

so, how to count numerical and string in php? i am really new in php thanks for helping and i hope suggestion from our programmers here. Sorry for my bad English.

i already found the answer, yes thanks for chris 85, strlen is not problem but the problem is in controller, this is i change my code :

if ( $username != '' && $password != '' && intval($group) > 0 && !$exist)
        {
            $myFunctions    = new userFunctions;
            $exist = $myFunctions->isUserNameExist( $username );
            $isValid = $myFunctions->isValidPassword( $password );
            $checkUsername = strlen($username);
            // var_dump($checkUsername); die();

            if ( $isValid == 0 && !$exist && $checkUsername <= 20)
            {
                $result = $myFunctions->saveNewUser( $username, $password, $group, $expired );
                $error =  ( $result ) ? 0 : 1;
            }
            elseif ($checkUsername > 20 ) 
            {
                $error = 99;
            } 
            else if( $exist )
            {
                $error = 3;
            }
            else $error = 2;
        }

and in the view like this :

function saveNewUsers()
                {
                    $.ajax({
                                type     :'POST',
                                dataType : 'json',
                                data     : { id: $('#hiUserID').val(), username : $('#txtUsername').val(), password: $('#txtPassword1').val(), group: $('#cbUserGroup').val(), expired: $('#cbExpired').val() },
                                url  : '" . \Yii::$app->getUrlManager()->createAbsoluteUrl('useraccount/saveuser') . "',
                                success  : function(response) {
                                    if ( !response.result ) {
                                        if ( response.error == 2 )
                                        {
                                            $('#errorMessageUser').html(DecodeEntities('{$myLabels[20]}.')).show();
                                        }
                                        else if( response.error == 3 )
                                        {
                                            $('#errorMessageUser').html(DecodeEntities('{$myLabels[56]}.')).show(); 
                                        }
                                        else if( response.error == 99)
                                        {
                                            $('#errorMessageUser').html(DecodeEntities('{$myLabels[57]}.')).show();     
                                        }
                                        else $('#errorMessageUser').html(DecodeEntities('{$myLabels[22]}.')).show();
                                    }
                                    else {      
                                        $('#errorMessageUser').html('').hide();
                                        $('#myUserModal').modal('hide');
                                        $.pjax.reload({container:'#myPjax',timeout:false});
                                    }   
                                }                       
                    });
                }

thanks for helping, finally i get the answer.