8.4. Chapter Review

When do you want to use an array rather than just a bunch of individually named variables?
Before writing a program, must you know the exact size of an array that you are going to create?
Before creating a new array in a program, must the program be able to calculate the proper size for the array?
After you have created the array, can you change the size of the original array object?
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?

Comment on the comparison between these two snippets:

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

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

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

Is this legal?

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

The definition of a program’s Main method may optionally include a parameter. What is the type? How is it used?
What is an alias? Why is understanding aliases important with arrays?
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.
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.

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]);

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]);

After this line, what is the value of a[2]?
```
bool[] a = new bool[5];
```

This will cause a runtime error. Why?

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

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

using System;

class ArrayLoop1
{  //Play computer on this code and then test
   public static void Main()
   {
      int[] a = {1, 2, 3}, b = {7, 2, 3, 5},
            c = {7, 0, 3, 2, 5};
      Console.WriteLine(foo(a, b, 2));
      Console.WriteLine(foo(c, b, 4));
   }

   static int foo(int[] x, int[] y, int n)
   {
      int k = 0;
      for (int i = 0; i < n; i++)
         if (x[i] == y[i]) {
            k++;
         }
      return k;
   }
}

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.

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

using System;

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

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.