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DocsAccept a bounded number
McBasic™ 0.7.881 · Build 881 · 5 min read
Hands-on tutorial · Input & events

Accept a bounded number

Work with a numeric value and validate its allowed range.

1 Form / control designs1 complete BASIC filesGuided sample project
Download complete projectComplete event code

Read Value for calculations rather than parsing a caption. Keep Minimum, Maximum and formatting consistent with the quantity being edited. Test an invalid intermediate edit as well as a final valid number: the user may temporarily leave a field empty while typing.

Step 1Prepare a safe practice project#

Extract the archive into a new writable folder, separate from your own application. Open NumericBox.mcbproj in McBasic™. Keep every declared source, layout, resource and migration file together.

To reconstruct it yourself, create a DesktopApp project and add the files declared below. In the complete project, follow these steps as a guided rebuild: replace each named source file once and Check after all its procedures are present.

Exact project configuration
project.mcproj
{
  "schemaVersion": 1,
  "projectId": "1dd54d1b-6179-493b-a173-137699b7bb89",
  "name": "NumericBoxSample",
  "kind": "DesktopApp",
  "ai": {
    "storeChatsInProject": false
  },
  "language": {
    "dialect": "McBasic1",
    "requireExplicit": true,
    "compare": "Binary",
    "defaultArrayBase": 0
  },
  "application": {
    "bundleIdentifier": "com.mcbasic.samples.numericbox",
    "version": "0.1.0",
    "buildNumber": "1",
    "startupFormId": "form-main",
    "shutdownMode": "OnStartupFormClosed"
  },
  "forms": [
    {
      "id": "form-main",
      "typeName": "frmMain",
      "layout": "Forms/frmMain.form.json",
      "code": "Forms/frmMain.bas"
    }
  ],
  "modules": [],
  "classes": [],
  "tests": [],
  "references": [],
  "resources": [],
  "targets": [
    "osx-arm64"
  ],
  "capabilities": []
}

Step 2Build the Form and set its properties#

frmMain

Select the Form first and set its properties. Add containers before their children. These are initial Designer values, not statements to paste into a procedure.

Form propertyValue
Caption"NumericBox — McBasic"
Width560
Height300
MinWidth440
MinHeight240
TypeNameParent
NumericBoxnumAmountForm
LabellblStatusForm
CommandButtoncmdCloseForm
numAmount · exact Inspector values
PropertyValue
Left48
Top72
Width220
Height34
Minimum-100
Maximum100
Value12.5
Increment0.5
DecimalPlaces1
ThousandsSeparatorTrue
Prefix"$ "
Suffix" USD"
Alignment"Right"
ReadOnlyFalse
Culture"Invariant"
TabIndex0
Anchor edgesLeft, Top
lblStatus · exact Inspector values
PropertyValue
Left48
Top128
Width460
Height36
Caption"Value: 12.5"
Anchor edgesLeft, Top
cmdClose · exact Inspector values
PropertyValue
Left48
Top192
Width140
Height36
Caption"Close"
TabIndex1
Anchor edgesLeft, Top

Step 3Connect the events explicitly#

frmMain

ObjectEventProcedureParameters
numAmountChangenumAmount_ChangeChange()
cmdCloseClickcmdClose_ClickClick()
FormLoadForm_Load()

Step 4Enter the complete behavior#

Open the named source file. Enter declarations first, then every procedure. Expand a procedure for its full body, or copy the complete file. Helpers are required: do not stop after entering the first Click handler.

Forms/frmMain.bas

Enter these declarations at file scope, before the procedures.

Forms/frmMain.bas · declarations
Option Explicit
Private Sub Form_Load()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmMain.bas · Form_Load
Private Sub Form_Load()
    numAmount.Minimum = -100
    numAmount.Maximum = 100
    numAmount.Value = 12.5
    numAmount.Increment = 0.5
    numAmount.DecimalPlaces = 1
    numAmount.ThousandsSeparator = True
    numAmount.Prefix = "$ "
    numAmount.Suffix = " USD"
    numAmount.Alignment = "Right"
    numAmount.ReadOnly = False
    numAmount.Culture = "Invariant"
    If numAmount.IsValid Then
        lblStatus.Caption = "Value: " & numAmount.Value
    Else
        lblStatus.Caption = numAmount.ValidationError
    End If
End Sub
Private Sub numAmount_Change()

Read the current value or selection and update its dependent interface. The binding above determines which object calls this handler.

Forms/frmMain.bas · numAmount_Change
Private Sub numAmount_Change()
    If numAmount.IsValid Then
        lblStatus.Caption = "Value: " & numAmount.Value
    Else
        lblStatus.Caption = numAmount.ValidationError
    End If
End Sub
Private Sub cmdClose_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmMain.bas · cmdClose_Click
Private Sub cmdClose_Click()
    Unload Me
End Sub
Copy the complete Forms/frmMain.bas file

Replace the file once; do not append duplicate procedures.

Forms/frmMain.bas
Option Explicit

Private Sub Form_Load()
    numAmount.Minimum = -100
    numAmount.Maximum = 100
    numAmount.Value = 12.5
    numAmount.Increment = 0.5
    numAmount.DecimalPlaces = 1
    numAmount.ThousandsSeparator = True
    numAmount.Prefix = "$ "
    numAmount.Suffix = " USD"
    numAmount.Alignment = "Right"
    numAmount.ReadOnly = False
    numAmount.Culture = "Invariant"
    If numAmount.IsValid Then
        lblStatus.Caption = "Value: " & numAmount.Value
    Else
        lblStatus.Caption = numAmount.ValidationError
    End If
End Sub

Private Sub numAmount_Change()
    If numAmount.IsValid Then
        lblStatus.Caption = "Value: " & numAmount.Value
    Else
        lblStatus.Caption = numAmount.ValidationError
    End If
End Sub

Private Sub cmdClose_Click()
    Unload Me
End Sub

Step 5Keep resources and storage reproducible#

No external resource or migration files are declared. Any inline migration, seed data or local JSON is present in the code above. Runtime application data and private preferences are not included in the archive.

Step 6Check, run and test the result#

Save all files and run Check. Resolve diagnostics before Run. Developer CLI users can work from the extracted folder:

Developer CLI
mcbasic check NumericBox.mcbproj
mcbasic run NumericBox.mcbproj

Acceptance checklist

  • Change the number using the keyboard and spinner.
  • Try values at the configured minimum and maximum.
  • Clear the entry and inspect validation behavior.

Step 7Make one change and repeat the tests#

Use the value in a calculated total and update the total from Change.

Save a working Git checkpoint first. Change one behavior, Check again and repeat the acceptance checklist. Compare with the downloaded solution if a regression appears.

Source baseline 20f4bfed6b · Build manifest