Collections of Game Objects - Learning C# by Programming Games - page 186

• The == operator is redefined and does the same as the Equals method. This is a

smart move: without this redefinition, the == operator would compare the refer-
ences and not the content of the objects. There are situations where two string
references to different object contain the same value. Thanks to the redefinition
the comparison will then still yield true . In languages such as Java and C this is
not done, so you have to watch out when you are comparing strings.

With the SubString method you can select a part of the string, for example the first
five characters:

string head;
head = s.SubString(0,5);

The numbering of the positions in a string is—just like arrays and lists—a bit spe-
cial: the first character is position 0, the second character position 1, and so on. As
parameters to the SubString method, you provide the position of the first character
that you need, and the position of the first character that you do not want anymore.
Therefore, the call s.SubString(0,5) gives the characters at positions 0, 1, 2, 3, and 4;
in other words the first five characters.
Just like arrays, you can access the individual elements in a string using an in-
dexer . However, you cannot change this element since the string type is immutable.
The individual elements of a string are of the primitive char type, so you can store
them directly in a variable:

char first;
first = s[0];

12.10 foreach : Do Something with All the Items in a List or an
Array

Traversing a list to perform some operation on each item in the list is so common,
that for that purpose, a special iteration instruction is available called foreach .For
example, the following foreach -instruction draws all the snowflakes in the list on the
screen:

foreach (Snowflake s in snowflakes)
s.Draw(gameTime, spriteBatch);

The foreach -instruction does away with the counter variable altogether. In each it-
eration, a local variable s represents the item that we are currently working on. Al-
though this is a very compact notation for iterating through a list, it is less powerful
than the full-fledged for -instruction, since we do not have control over which items
in the list are processed and in which order. The foreach -instruction can be used on
both arrays and lists. Here is the syntax diagram for the foreach -instruction: