10.9. Chapter Review Questions¶

1. When do you want to use an array rather than just a bunch of individually named variables?

2. Before writing a program, must you know the exact size of an array that you are going to create?

3. Before creating a new array in a program, must the program be able to calculate the proper size for the array?

4. After you have created the array, can you change the size of the original array object?

5. If I have the declaration

   int[] vals = new int[5];
   

   1. What is stored directly in the memory position for variable vals?
   2. Does vals[3] then have a clear value? If so, what?
   3. Can I later make vals refer to an array of a different size?

6. Comment on the comparison between these two snippets:

   char[] a = {'n', 'o', 'w'};
   a[0] = 'c';
   
   string s = "now";
   s[0] = 'c';
   

7. If I want to read or modify the first 100 elements of a 999 element array, would I use a foreach loop or a for loop? Explain.

8. If I want to modify all the elements of an array, would I use a foreach loop or a for loop? Explain.

9. If I want to read all the elements of an array, but not change the array, and I do not care about the exact position in the array of any member, would I use a foreach loop or a for loop?

10. Is this legal?

    int[] a= {1, 2, 3, 4};
    //...
    a = new int[7];
    

11. The definition of a program’s Main method may optionally include a parameter. What is the type? How is it used?

12. What is an alias? Why is understanding aliases important with arrays?

13. If I have a function declared

    static void f(int num)
    //...
    

    and I call it from my Main function

    int v = 7;
    f(v);
    Console.WriteLine(v);
    

    Could f change the value of the variable v, so 1 is printed in Main? If so, write a one-line body for f that does it.

14. If I have a function declared

    static void f(int[] nums)
    //...
    

    and I call it from my Main function

    int[] v = {7, 8, 9};
    f(v);
    Console.WriteLine(v[0]);
    

    Could f change the value of the variable v[0], so 1 is printed in Main? If so, write a one-line body for f that does it.

15. What is printed by this snippet?

    int[] a = {1, 2, 3};
    int[] b = {4, 5, 6};
    b[0] = 7;
    a[1] = 8;
    b[2] = 9;
    Console.WriteLine("" + a[0] + a[1] + a[2]);
    

16. What is printed by this snippet? (Only the second line is changed.)

    int[] a = {1, 2, 3};
    int[] b = a;
    b[0] = 7;
    a[1] = 8;
    b[2] = 9;
    Console.WriteLine("" + a[0] + a[1] + a[2]);
    

17. If my only use for variable temp is to set up this call to f:

    int[] temp = {1, 2, 3};
    f(temp);
    

    how could I rewrite it with an anonymous array?

18. After this line, what is the value of a[2]?

    bool[] a = new bool[5];
    

19. This will cause a runtime error. Why?

    string[] a = new string[5];
    foreach(string s in a) {
       Console.WriteLine(s.Length);
    }
    

20. If you get a data sequence from a Random object, is it really random?

21. Explain the significance of a seed for a Random object.

22. Suppose I create an object table of type double[,], and I think of the first index as referring to a row and the second index as referring to a column.

    1. Must each row be the same length?
    2. Does each row have a type double[] ?

23. (Optional) Suppose I create an object table of type double[][], and I think of the first index as referring to a row and the second index as referring to a column.

    1. Must each each row be the same length?
    2. Does each row have a type double[] ?