如何从 Ienumerable 返回一个字符串？

Question

I am very new to programming and am taking an Object Oriented Programming class. However, the professor didn't explain how to take an Ienumerable and make it into a string in order to accomplish this question of the assignment:

TODO: Write a public static C# method named NumSquare that takes a one-dimentional array as input and creates a LINQ statement that queries the numbers that have a square number graeter than 20 and orders them ascending. The LINQ query retrieves anonymous objects in which each object contains the number (Num) and its square number (SqrNum). The method returns the LINQ query as an IEnumerable object. The anonymous object contains two instance variables named Num and SqrNum. Input: a one-dimentional integer array. Output: a LINQ query of type IEnumerable. Example: Given array A = [3, 4, 10, 5], invoking NumSquare(A) return a LINQ query that once executed will contain: {Num=5, SqrNum=25}, {Num=10, SqrNum=25}

Here's what I have so far, but I've tried several things over the last 2 1/2 weeks.

        public static IEnumerable<object> NumSquare(int[] A)
        {
            //write your code here

            var num = from Number in A
                      select Number;
            var sqrnum = from Number in A
                         let squarenum = Number * Number
                         select squarenum;
            
            return (IEnumerable<object>)sqrnum;
        }

I know that this return won't get me the whole result that I need, but that's as far as I can get with no errors. I also don't know how to test anything because he didn't show us how to call an IEnumerable. Help?

Answer 1

I think what you are looking for is not a string as output but as the exercise says an anonymous object. An anonymous object can be something like this:

var o = new { Num = 4, SqrNum = 16 };

Its just an object that basically has no explicit type and some read-only variables.

So what you want to do is to convert your array into a IEnumerable<{int Num, int SqrNum}> which you would have to declare as IEnumerable<object> and not a string.

You could do something like this:

static IEnumerable<object> NumSqr(int[] a)
{
    return a
        .Where(x => x * x > 20)
        .OrderBy(x => x)
        .Select(x => new { Num = x, SqrNum= x * x });
}

Alternatively:

static IEnumerable<object> NumSqr(int[] a)
{
    return from number in a
        where number * number > 20
        orderby number
        select new { Num = number, SqrNum = number * number };
}

In order to print out the result of the function you could do this:

var a = new int[] { 3, 4, 10, 5 };
var result = NumSqr(a);
foreach (var obj in result)
{
    Console.WriteLine(obj);
}

The output should look like this:

{ Num = 5, SqrNum = 25 }
{ Num = 10, SqrNum = 100 }