Example of "counter" entity in Durable Functions.

counter-entity.cs

public static async Task Counter(
    [EntityTrigger] IDurableEntityContext ctx)
{
    int currentValue = ctx.GetState<int>();

    switch (ctx.OperationName)
    {
        case "add":
            int amount = ctx.GetInput<int>();
            currentValue += amount;
            break;
        case "reset":
            currentValue = 0;
            break;
        case "get":
            ctx.Return(currentValue);
            return;
    }

    ctx.SetState(currentValue);
}