Custom API for numeric formulas

[Steelman70]

Hello, following this great post and substituting the C# code with the below (no changes required to the JSON code) I have created a function that returns the factorial of any integer between 0 and 170 or returns -1 if the input is not an integer or out of the range.

The problem is that the number is returned as a string.  Could anyone suggest any changes to the C# and JSON code to make this happen?  I have tried to change the "string" to "number" and "double" in both the C# and JSON but it has not worked.

using System.Net;

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    log.Info($"C# HTTP trigger function processed a request. RequestUri={req.RequestUri}");

    // parse query parameter
    string name = req.GetQueryNameValuePairs()
        .FirstOrDefault(q => string.Compare(q.Key, "name", true) == 0)
        .Value;

    // Get request body
    dynamic data = await req.Content.ReadAsAsync<object>();

    // Set name to query string or body data
    name = name ?? data?.name;

     // Initialise the return variable
    double factorial = -1;
    
    // Convert the input to a short integer and calculate factorial.  Result is -1 if input is not an integer between 0 and 170
    ushort n;
    if (ushort.TryParse(name, out n))
    {
        if (n <= 170)
        // If input is >170 then it will be out of range for double type variable    
        {        
            if (n == 0)        
          {
                factorial = 1;
                // Factorial of 0 is 1
         }        
            else        
           {
              int numberInt = n;
                factorial = n;
                for (int i = 1; i < n; i++)
                    {
                        factorial = factorial * i;
                   }
            }        
      }        
    }
    return req.CreateResponse(HttpStatusCode.OK, factorial.ToString());
    // return the result as a string since I don't know how to return a number to PowerApps
}

[dtsiniavskyi]

Just make your api action to return int instead of HttpResponseMessage. So it will be treated as int in your powerapp. Because content of your HttpResponseMessage will always be non generic object and you wont know the actual type of it's properties in the powerapp.

[Steelman70]

dtsiniavskyi, thank you.  Apologies but I am just a beginner in APIs.  Should I just replace HttpResponseMessage with int in the C# code like this?

public static async Task<int> Run(HttpRequestMessage req, TraceWriter log)

Any changes to the JSON?

Also, because the factorial returns large numbers, I would ideally need to be able to return a double.

[dtsiniavskyi]

Yes, just replace HttpResponseMessage with the type you need. I know for sure that int can be returned easily and it will be recognized as a number within your powerapp, not sure about double, but you could try. Maybe decimal will be the best option.

[Steelman70]

The Azure function compiler gives me this...

2016-05-31T15:36:38.572 run.csx(53,12): error CS0029: Cannot implicitly convert type 'System.Net.Http.HttpResponseMessage' to 'int'
2016-05-31T15:36:38.572 Compilation failed.

PS I can easily make the C# return a double by just removing the .ToString() in the third but last line, but then PowerApps will not show any result 

[dtsiniavskyi · Accepted solution]

using System.Net;

public static async Task<decimal> Run(HttpRequestMessage req, TraceWriter log)
{
    log.Info($"C# HTTP trigger function processed a request. RequestUri={req.RequestUri}");

    // parse query parameter
    string name = req.GetQueryNameValuePairs()
        .FirstOrDefault(q => string.Compare(q.Key, "name", true) == 0)
        .Value;

    // Get request body
    dynamic data = await req.Content.ReadAsAsync<object>();

    // Set name to query string or body data
    name = name ?? data?.name;

     // Initialise the return variable
    double factorial = -1;
    
    // Convert the input to a short integer and calculate factorial.  Result is -1 if input is not an integer between 0 and 170
    ushort n;
    if (ushort.TryParse(name, out n))
    {
        if (n <= 170)
        // If input is >170 then it will be out of range for double type variable    
        {        
            if (n == 0)        
          {
                factorial = 1;
                // Factorial of 0 is 1
         }        
            else        
           {
              int numberInt = n;
                factorial = n;
                for (int i = 1; i < n; i++)
                    {
                        factorial = factorial * i;
                   }
            }        
      }        
    }
    return (decimal)factorial;
}

That's how I think your api action should look. 

[Steelman70 · Accepted solution]

I played around a bit and the final few lines of the JSON file need to be edited as follows.  Not only does the "string" need to be substituted with "integer", but also "format": "int32" needs to be added.

      "responses": {
          "200": {
            "description": "Successful response",
            "schema": {
              "title": "The response of the api.",
              "type": "integer",
              "format": "int32"
            }
          }
        }