Example of InOut Parameter in custom workflow

using Microsoft.Xrm.Sdk;
using Microsoft.Xrm.Sdk.Query;
using Microsoft.Xrm.Sdk.Workflow;
using System;
using System.Activities;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ClassLibrary1
{
    public class Program : CodeActivity
    {

        [Input("Value")]
        public InArgument<string> Value { get; set; }
        [Output("AccountId")]
        public OutArgument<string> AccountId { get; set; }
        protected override void Execute(CodeActivityContext context)
        {
            IWorkflowContext wfcontext = context.GetExtension<IWorkflowContext>();
            IOrganizationServiceFactory serviceFactory = context.GetExtension<IOrganizationServiceFactory>();
            IOrganizationService service = serviceFactory.CreateOrganizationService(wfcontext.InitiatingUserId);
            Entity Contact = service.Retrieve(wfcontext.PrimaryEntityName, wfcontext.PrimaryEntityId, new ColumnSet(""));
            if (Contact.Contains("parentcustomerid"))
            {
                string accounid = (Contact["parentcustomerid"] as EntityReference).Id.ToString();
                AccountId.Set(context, accounid);
            }
            string erfUser = Value.Get<string>(context);
        }
    }
}