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C# C# Collections Arrays Jagged Arrays

Scott Kim
Scott Kim
518 Points

Jagged Array Challenge - hard to tell what I am doing...please help!

I keep getting errors regarding = inn lines 12 and 14, but no clues. Can anyone please help?

Math.cs
namespace Treehouse.CodeChallenges
{
    public static class MathHelpers
    {
        public static int[][] BuildMultiplicationTable(int maxFactor)
        {
            int arraySize = maxFactor + 1;
            int[][] BuildMultiplicationTable = new int[arraySize][];

            BuildMultiplicationTable[arraySize] = new int[arraySize];

            for (int i=0, i < maxFactor; i++)
            {
                for (int j=0, j < maxFactor; j++)
                {
                    table[i][j] = i * j;
                }
            }

            return table;

        }
    }
}

4 Answers

You have a comma instead of a semicolon in for (int i=0, i < maxFactor; i++) and for (int j=0, j < maxFactor; j++). You also have not declared table.

Scott Kim
Scott Kim
518 Points

Aha - thanks! My update as follows, but it says..."Bummer: Index was outside the bounds of the array."

namespace Treehouse.CodeChallenges { public static class MathHelpers { public static int[][] BuildMultiplicationTable(int maxFactor) { int arraySize = maxFactor + 1; int[][] BuildMultiplicationTable = new int[arraySize][];

        BuildMultiplicationTable[arraySize] = new int[arraySize];

        for (int i=0; i < maxFactor; i++)
        {
            for (int j=0; j < maxFactor; j++)
            {
                BuildMultiplicationTable[i][j] = i * j;
            }
        }

        return BuildMultiplicationTable;

    }
}

}

In the line BuildMultiplicationTable[arraySize] = new int[arraySize];, arraySize is outside the bounds of the array because the indices start at 0 and go to arraySize-1. If you used maxFactor as the index instead, then it would only set the dimension of the last inner array. To set the dimension of each of the inner arrays, you could instead define the size of each inner array inside the outer for loop by setting the index to i.

In both the for loops, you might want to change from the form i < maxFactor to i <= maxFactor or i < arraySize so that maxFactor is included in the calculations.

Scott Kim
Scott Kim
518 Points

Thanks so much JB! I tried again, but the same error I got...any clue may I ask? Thanks a bunch!

==

namespace Treehouse.CodeChallenges { public static class MathHelpers { public static int[][] BuildMultiplicationTable(int maxFactor) { int[][] BuildMultiplicationTable = new int[maxFactor][];

        BuildMultiplicationTable[maxFactor] = new int[maxFactor];

        for (int i=0; i <= maxFactor; i++)
        {
            for (int j=0; j <= maxFactor; j++)
            {
                BuildMultiplicationTable[i][j] = i * j;
            }
        }

        return BuildMultiplicationTable;

    }
}

}

In the line int[][] BuildMultiplicationTable = new int[maxFactor][];, the number of arrays in the first dimension of BuildMultiplicationTable is set to maxFactor. Based on the challenge example output, the challenge is expecting there to be maxFactor + 1 arrays in the first dimension of BuildMultiplicationTable. Try changing it back to int[][] BuildMultiplicationTable = new int[maxFactor + 1][];

If BuildMultiplicationTable has at least maxFactor + 1 elements in its first dimension, then the line BuildMultiplicationTable[maxFactor] = new int[maxFactor]; sets the length of an array at BuildMultiplicationTable[maxFactor]. It does not set the length of an array at any other index of BuildMultiplicationTable. For example, if maxFactor is not 0, the length of an array at BuildMultiplicationTable[0] has not been defined, so any index j for BuildMultiplicationTable[0][j] will be outside the bounds of the array BuildMultiplicationTable[0].

You could use a for loop to define each of the arrays in the array BuildMultiplicationTable by

for (int i = 0; i <= maxFactor; i++)
{
    BuildMultiplicationTable[i] = new int[maxFactor + 1];
}

which defines the length of an inner array at each element of the first dimensional array in BuildMultiplicationTable.

Scott Kim
Scott Kim
518 Points

Aaaaaah, now I get it!! (And it worked out!) THANK YOU SO VERY MUCH JB!!!

Scott Kim
Scott Kim
518 Points

For anyone curious about how this ended with JB's help.

==

namespace Treehouse.CodeChallenges { public static class MathHelpers { public static int[][] BuildMultiplicationTable(int maxFactor) { int[][] BuildMultiplicationTable = new int[maxFactor + 1][]; for (int i=0; i <= maxFactor; i++) { BuildMultiplicationTable[i] = new int[maxFactor+ 1 ];

                for (int j=0; j <= maxFactor; j++)
                {
                    BuildMultiplicationTable[i][j] = i*j;
                }
        }

        return BuildMultiplicationTable;
    }
}

}