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C# C# Collections Lists Lists

Aaron Selonke
Aaron Selonke
10,323 Points
Posted by Aaron Selonke
Aaron Selonke
10,323 Points

Getting Past the C# List<T> Challange

The code below works fine in the IDE, but will not let me pass the challenge.

Directions: "Create a static method named GetPowersOf2 that returns a list of powers of 2 from 0 to the value passed in. So if 4 was passed in, the function would return { 1, 2, 4, 8, 16 }. The System.Math.Pow method will come in handy."

Error: " Bummer! Does MathHelpers.GetPowersOf2 return List`1?"

Does anyone now what the Code Challenge is looking for (besides what its asking)

Thanks

MathHelpers.cs 
using System.Collections.Generic;
using System;

namespace Treehouse.CodeChallenges
{
    public static class MathHelpers
    {
        public static List<double> GetPowersOf2(int input)
        {
            var returnList = new List<double>();
            for (int i = 0; i < input+1; i++)
            {
                returnList.Add(Math.Pow(2, i));
            }
            return returnList;

        }

    }
}

10 Answers

Zachary Steiger
Zachary Steiger
21,391 Points

The challenge is confusing in that it wants the List returned to the method to be of type int, however Math.Pow() uses type double for its parameters. Your solution above is close, all you have to do is change each instance of List<double> to List<int> and then use typecasting on your Math.Pow() method, as seen below

for(int i = 0; i <= input; i++)
{
    returnList.Add((int)Math.Pow(2, i))
}
Rui Martinho
Rui Martinho
21,221 Points
Rui Martinho
Rui Martinho
21,221 Points

It worked.

Thank you, Zachary

Aaron Selonke
Aaron Selonke
10,323 Points
Aaron Selonke
Aaron Selonke
10,323 Points

Nice, You can read a code challenge - there was nothing that would have made me guess that it is expecting a list of int.

ravindrareddy
ravindrareddy
10,590 Points
ravindrareddy
ravindrareddy
10,590 Points

I do not see any issue in the code. But try declaring the List<double> returnList = new List<double>(); instead of var. Also try if the code may be validating for a List of intergers. try converting the power to an integer and then store it to the List of Intergers than double values.

Alexander Davison
Alexander Davison
65,469 Points

Nice catch! :)

Jabran Noor
Jabran Noor
32,306 Points
Jabran Noor
Jabran Noor
32,306 Points

Try using for(int i=0; i <= input; i++)

Alexander Davison
Alexander Davison
65,469 Points

Actually,

for (int i = 0; i < input + 1; i++)

And

for (int 1 = 0; i <= input; i++)

Are exactly the same.

Martin Sole
Martin Sole
82,199 Points
Martin Sole
Martin Sole
82,199 Points

I had the same issue, but managed to pass the challenge by using int for the list type instead of double and casting the returnList to an int, 

returnList.Add((int)Math.Pow(2, i));
Alexander Davison
Alexander Davison
65,469 Points
Alexander Davison
Alexander Davison
65,469 Points

I'm rather new to C#, but maybe try getting rid of the +1 from this: for (int i = 0; i < input+1; i++)

Good luck! ~Alex

Rui Martinho
Rui Martinho
21,221 Points
Rui Martinho
Rui Martinho
21,221 Points

I am experiencing the same problem.

It returns the message "Error: " Bummer! Does MathHelpers.GetPowersOf2 return List`1?""

gregsmith5
gregsmith5
32,615 Points
gregsmith5
gregsmith5
32,615 Points

I've also got the same problem and almost identical code. When I compile and run locally, it produces a list of doubles with the correct values, so it seems to be a bug in the challenge. Has anyone reported it yet?

Chanuka Weerasinghe
Chanuka Weerasinghe
2,337 Points
Chanuka Weerasinghe
Chanuka Weerasinghe
2,337 Points

Just adding this answer even after 4 months because I had the same issue and came here to see if there was a bug in the task. Lol

Just to cofirm no bug in this task. Although poorly written question as it seems.

This is the complete solution - 

        int num = Convert.ToInt32(userInput);

        List <int> numList = new List <int>();

        for (int x = 0; x <= num; x++)
        {
            numList.Add((int)Math.Pow(2, x));
        }

return numList;

Sara Rena Anderson
Sara Rena Anderson
15,045 Points
Sara Rena Anderson
Sara Rena Anderson
15,045 Points 
using System.Collections.Generic;
using System;

namespace Treehouse.CodeChallenges
{
    public static class MathHelpers
    {
        public static List<int> GetPowersOf2(int input)
        {
            var returnList = new List<int>();
        for(int i = 0; i <= input; i++)
        {
            returnList.Add((int)Math.Pow(2, i));
        }
            return returnList;

        }

    }
}
Kevin Gates
Kevin Gates
15,053 Points
Kevin Gates
Kevin Gates
15,053 Points

Alternate solution:

using System.Collections.Generic;
using System;
namespace Treehouse.CodeChallenges
{
    public static class MathHelpers
    {
        public static List<int> GetPowersOf2 (int value)
        {
            List<int> returnList = new List<int>(value+1);
            for (int i = 0 ; i < returnList.Capacity; i++)
            {
                returnList.Add(Convert.ToInt32(Math.Pow(2, i)));
            }
            return returnList;
        }
    }
}