c# loop through json data

You could use the DataContractJsonSerializer class that's part of the System.Runtime.Serialization assembly. Start by writing a model that will represent this entity:

public class MyModel
{
    public decimal Demand { get; set; }
    public decimal Supply { get; set; }
    public DateTime Date { get; set; }
    public string DateString { get; set; }
}

and then deserialize the JSON string to a list of this model:

string json = "[{ \"Demand\": 4422.45, \"Supply\": 17660, \"Date\": \"/Date(1236504600000)/\", \"DateString\": \"3 PM\" },  { \"Demand\": 4622.88, \"Supply\": 7794, \"Date\": \"/Date(1236522600000)/\", \"DateString\": \"8 PM\" }, { \"Demand\": 545.65, \"Supply\": 2767, \"Date\": \"/Date(1236583800000)/\", \"DateString\": \"1 PM\" }, { \"Demand\": 0, \"Supply\": 1, \"Date\": \"/Date(1236587400000)/\", \"DateString\": \"2 PM\" }]";
DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(List<MyModel>));
using (Stream stream = new MemoryStream(Encoding.UTF8.GetBytes(json)))
{
    List<MyModel> models = (List<MyModel>)serializer.ReadObject(stream);
    foreach (MyModel model in models)
    {
        // do something with the model here
        Console.WriteLine(model.Date);
    }
}

UPDATE:

It looks like you are using some prehistoric version of C# which doesn't support auto properties. In this case you will need a private field for each property:

public class MyModel
{
    private decimal demand;
    public decimal Demand 
    { 
        get { return this.demand; }
        set { this.demand = value; }
    }

    private decimal supply;
    public decimal Supply 
    { 
        get { return this.supply; }
        set { this.supply = value; }
    }

    private DateTime date;
    public DateTime Date
    { 
        get { return this.date; }
        set { this.supply = value; }
    }

    private string dateString;
    public string DateString
    { 
        get { return this.dateString; }
        set { this.dateString = value; }
    }
}

Another approach it would be to use the JavaScriptSerializer, which is part of the System.Web.Extensions assembly.

You will need a model, that represents your data:

public class Data
{
    public decimal Demand { get; set; }
    public int Supply { get; set; }
    public DateTime Date { get; set; }
    public string DateString { get; set; }
}

Then you just need this:

string json = "[{\"Demand\": 4422.45,\"Supply\": 17660,\"Date\":\"\\/Date(1236504600000)\\/\",\"DateString\":\"3 PM\" },{\"Demand\": 4622.88, \"Supply\": 7794, \"Date\": \"\\/Date(1236522600000)\\/\", \"DateString\": \"8 PM\" }]";
JavaScriptSerializer serializer = new JavaScriptSerializer();
List<Data> result = serializer.Deserialize<List<Data>>(json);

Note: Please note that Date property in the json. I added some extra characters: \"\\/Date(1236504600000)\\/\". Unfortunately, neither DataContractJsonSerializer nor JavaScriptSerializer can deserialize "/Date(1236504600000)/", you need defenitely these extra characters. If you are the producer and the consumer of this json, then you can handle this in client fairly easily as it is described here. Otherwise some similar approach should be followed server side, before you deserialize the json that client sends to you.