// Create new project and extended attribute definition
System::SharedPtr<Project> project = System::MakeObject<Project>();
    
System::SharedPtr<ExtendedAttributeDefinition> attribute = ExtendedAttributeDefinition::CreateTaskDefinition(Aspose::Tasks::CustomFieldType::Cost, Aspose::Tasks::ExtendedAttributeTask::Cost1, u"");
attribute->set_Formula(u"[Cost]-[Actual Cost]");
    
project->get_ExtendedAttributes()->Add(attribute);
    
// Add task
System::SharedPtr<Task> task = project->get_RootTask()->get_Children()->Add(u"Task");
    
// Create extended attribute
System::SharedPtr<ExtendedAttribute> extendedAttribute = attribute->CreateExtendedAttribute();
task->get_ExtendedAttributes()->Add(extendedAttribute);
    
// Display if extended attributes are read only or not
System::Console::WriteLine(extendedAttribute->get_ValueReadOnly() == true ? System::String(u"Value is Read only") : System::String(u"Value is not read only"));
extendedAttribute->set_NumericValue(-System::Decimal(1000000));
System::Console::WriteLine(extendedAttribute->get_NumericValue() == -System::Decimal(1000000) ? System::String(u"Formula values are read-only") : System::String(u"Values are not read-only"));