Multiple Choices

1. What is the correct way of creating a 2-dimensional rectangular array of int with 5 rows and 2 columns named myMatrix?

   • int[][] myMatrix = new int[5][2];
   • int[][] myMatrix = new int[2][5];
   • int[,] myMatrix = new int[2, 5];
   • int[,] myMatrix = new int[5, 2];

2. Consider the following code:

   int[,] grades = {{10, 20}, {30, 40}};
   Console.WriteLine(grades[1,0]);

   What will it display?

   • Nothing
   • 10
   • 20
   • grades
   • 30
   • grades[1,0]
   • 40

Exercises

1. Write a statement that creates a 2-dimensional rectangular array of int with 5 rows and 3 columns.

   Solution

    int[,] matrix = new int[5, 3];

2. Write a statement that creates a 2-dimensional jagged array of int with 2 rows. The first row should contain an array containing 1, the second row should contain an array containing 2, 3.

   Solution

    int[][] jaggedArray = new int[2][];
    jaggedArray[0] = new int[1] { 1 };
    jaggedArray[1] = new int [2]{ 2, 3};

3. Write a declaration for a 2-dimensional rectangular array of int containing the following data:

   10	20	30
   40	50	60
   70	80	90

    <details>

   Solution

   int[,] matrix =
       {
           {10, 20, 30},
           {40, 50, 60},
           {70, 80, 90}
       };

4. Write a declaration for a 2-dimensional ragged array of int containing the following data:

   10	20
   40
   70	80	90

   Solution

    int[][] data = new int[3][];
    data[0] = new int[3] { 10, 20, 30 };
    data[1] = new int[1] { 40 };
    data[2] = new int[3] { 70, 80, 90 };

5. Suppose we have a 2-dimensional rectangular array named temp that has been declared and initialized. How can we know the number of rows in this array?

   Solution

   By using the GetLength method: temp.GetLength(0) is the number of rows in the temp array.

6. Suppose we have a 2-dimensional rectangular array named temp that has been declared and initialized. How can we know the number of elements in this array?

   Solution

   By using the Length field: temp.Length is the number of elements in the temp array. We can also compute the product of temp.GetLength(0) and temp.GetLength(1).

7. Write a program that display “Every row contains its own index” if the 2-dimensional rectangular array of int matrix is such that its first row contains the value 0, its second row contains the value 1, etc.

   Solution

    bool foundIndex = true;
    for (int row = 0; row < matrix.GetLength(0); row++)
    {
        if(row == 0 || foundIndex)
        {
            foundIndex = false;
            for (int col = 0; col < matrix.GetLength(1); col++)
            {
                if (matrix[row, col] == row) {
                    foundIndex = true;
                }
            }
        }
    }
    
    if(foundIndex){
        Console.WriteLine("Every row contains its own index");
    }

8. Write a program that display the average of each row of a 2-dimensional jagged array of int jArray.

   Solution

    double sum;
    for(int i = 0; i < jArray.Length; i++)
    {
        sum = 0;
        for (int j = 0; j < jArray[i].Length; j++)
        {
            sum += jArray[i][j];
        }
        Console.WriteLine("Average for row #" + i
            + " is " + sum / jArray[i].Length);
    }

9. Write a program that display the sum of the values on the diagonal of a 2-dimensional rectangular array of int jArray.

   Solution

    int sum = 0;
    for (int i = 0; i < matrix.GetLength(0); i++)
    {
        sum += matrix[i, i];
    }
    Console.WriteLine(sum);

Problem: Toward a Crossword Puzzle Solver

The goal of this problem is to work toward the creation of a program that solve crossword puzzles. We will reason in the simple case where the “word” is actually simply a pair of number (so, “1, 2” or “8, 101”).

In the following, assume given two int variables first and second, as well as a 2-dimensional rectangular array values.

1. Write a program that display “pair found” if first and second occur next to each other in the same row.
2. Edit your program so that “pair found” is displayed also if second occurs before first in the same row.
3. Edit your program so that “pair found” is displayed also if first occurs “above” second (that is, if they are next to each other in the same column),
4. Edit your program so that “pair found” is displayed also if second occurs “above” first,
5. Edit your program so that “pair found” is displayed also if first and second occur diagonally,
6. Edit your program so that “pair found” is displayed also if first and first occur anti-diagonally.

Test your program thoroughly, possibly bundling it in a static class to ease testing and debugging.