Chapter Review

6.5. Chapter Review#

  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?

  1. Comment on the comparison between these two snippets:

    char[] a = {'n', 'o', 'w'};
    a[0] = 'c';

    string s = "now";
    s[0] = 'c';

  1. 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.

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

  3. 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?

  4. Is this legal?

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

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

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

  3. If I have a method declared:

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

and I call it from my `Main` method:

    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.

  1. If I have a method declared

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

and I call it from my `Main` method:

    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.

  1. 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]);

  1. 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]);

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

    bool[] a = new bool[5];

  1. This will cause a runtime error. Why?

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

  1. What is printed by this program? Play computer first to figure out.

     1using System;
 2
 3class ArrayLoop1
 4{  //Play computer on this code and then test
 5   public static void Main()
 6   {
 7      int[] a = {1, 2, 3}, b = {7, 2, 3, 5},
 8            c = {7, 0, 3, 2, 5};
 9      Console.WriteLine(foo(a, b, 2));
10      Console.WriteLine(foo(c, b, 4));
11   }
12
13   static int foo(int[] x, int[] y, int n)
14   {
15      int k = 0;
16      for (int i = 0; i < n; i++)
17         if (x[i] == y[i]) {
18            k++;
19         }
20      return k;
21   }
22}

    Then you can run example array_loop1/array_loop1.cs to check the results and see our table from playing computer included in the project, array_loop1/play_computer1.txt.

  2. What is printed by this program? Play computer first to figure out. Be careful to keep the data current!

     1using System;
 2
 3class ArrayLoop2
 4{  //Play computer on this code first and then test
 5   public static void Main()
 6   {
 7      int[] a =  {5, 7, 6, 9, 8};
 8      for (int i = 0; i < 3; i++) {
 9         a[i+2] = a[i];
10      }
11      foreach (int x in a) {
12         Console.Write(x);
13      }
14      Console.WriteLine();
15   }
16}

    Then you can run example array_loop2/array_loop2.cs to check the results and see our table from playing computer included in the project, array_loop2/play_computer2.txt.