Learn C# Programming - Nullables & Arrays

Learn C# Programming
Nullables & Arrays
Eng Teong Cheah
Microsoft MVP in Visual Studio &
Development Technologies

Agenda
•Nullables
•Arrays
•Strings
•Structure
•Enums

C# - Nullables
C# provides a special data types, the nullable types, to which you can
assign normal range of values as well as null values.
For example, you can store any value from -2,147,483,648 to 2,
147,483, 647 or null in a Nullable<Int32> variable. Similarly, you can
assign true, false, or null in a Nullable<bool> variable. Syntax for
declaring a nullable type is as follows:
< data_type> ? <variable_name> = null;

C# - Nullables
The Null Coalescing Operator(??)
The null coalescing operator is used with the nullable value types and
reference types. It is used for converting an operand to the type of
another nullable (or not) value type operand, where an implicit
conversion is possible.

C# - Arrays
An array stores a fixed-size sequential collection of elements of the
same type. An array is used to store a collection of data, but it is
often more useful to think of an array as a collection of variables of
the same type stored at contiguous memory locations.
Instead of declaring individual variables, such as number0, number1,
…, and number99, you declare one array variable such as numbers
and use numbers[0], numbers[1], and …, numbers[99] to represent
individual variables. A specific element in an array is accessed by an
index.

C# - Arrays
All arrays consist of contiguous memory locations. The lowest
address corresponds to the first element and the highest address to
the last element.

C# - Arrays
Declaring Arrays
To declare an array in C#, you can use the following syntax:
where,
datatype[] arrayName;

C# - Arrays
where,
- datatype is used to specify the type of elements in the array.
- [ ] specifies the rank of the array. The rank specifies the size of the
array.
- arrayName specifies the name of the array.
For example,
double[] balance;
Declaring Arrays

C# - Arrays
Initializing Arrays
Declaring an array does not initialize the array in the memory. When
the array variable is initialized, you can assign values to the array.
Array is a reference type, so you need to use the new keyword to
create an instance of the array. For example,
double[] balance = new double[10];

C# - Arrays
Assigning Values to an Array
You can assign values to individual array elements, by using the index
number, like:
You can assign values to the array at the time of declaration, as
shown:
double[] balance = new double[10];
balance[0] = 4500.0;
double[] balance = { 2340.0, 4523.69, 3421.0};

C# - Arrays
You can also create and initialize an array, as shown:
You may also omit the size of the array, as shown:
int [] marks = new int[5] { 99, 98, 92, 97, 95};
int [] marks = new int[] { 99, 98, 92, 97, 95};

C# - Arrays
You can copy an array variable into another target array variable. In
such case, both the target and source point to the same memory
location:
When you create an array, C# compiler implicitly initializes each array
element to a default value depending on the array type. For example,
for an int array all elements are initialized to 0.
int [] marks = new int[] { 99, 98, 92, 97, 95};
int[] score = marks;

C# - Arrays
Accessing Array Elements
An element is accessed by indexing the array name. This is done by
placing the index of the element within square brackets after the
name of the array. For example,
double salary = balance[9];

C# - Arrays
Using the foreach Loop
In the previous example, we used a for loop for accessing each array
element. You can also use a foreach statement to iterate through an
array.

C# - Arrays
There are following few important concepts related to array which
should be clear to a C# programmer:
- Multi-dimensional arrays
- Jagged arrays
- Passing arrays to functions
- Param arrays
- The Array Class

C# - Arrays
Multidimensional Arrays
C# allows multidimensional arrays. Multi-dimensional arrays are also
called rectangular array. You can declare a 2-dimensional array of
strings as:
or, a 3-dimensional array of int variables as:
string [,] names;
int [ , , ] m;

C# - Arrays
Multidimensional Arrays
Two-Dimensional Arrays
The simplest form of the multidimensional array is the 2-dimensional
array. A 2-dimensional array is a list of one-dimensional arrays.

C# - Arrays
A 2-dimensional array can be thought of as a table, which has x
number of rows and y number of columns. Following is a 2-
dimensional array, which contains 3 rows and 4 columns.

C# - Arrays
Thus, every element in the array a is identified by an element name
of the form a[i,j], where a is the name of the array, and i and j are the
subscripts that uniquely identify each element in array a.

C# - Arrays
Initializing Two-Dimensional Arrays
Multidimensional arrays may be initialized by specifying bracketed
values for each row. The following array is with 3 rows and each row
has 4 columns.
int [,] a = new int [3,4] {
{0, 1, 2, 3} , /* initializers for row indexed by 0 */
{4, 5, 6, 7} , /* initializers for row indexed by 1 */
{8, 9, 10, 11} /* initializers for row indexed by 2 */
};

C# - Arrays
Accessing Two-Dimensional Array Elements
An element in 2-dimensional array is accessed by using the
subscripts. That is, row index and column index of the array. For
example,
The above statement takes 4th element form the 3rd row of the array.
You can verify it in the above diagram.
int val = a[2,3];

C# - Arrays
Jagged Arrays
A Jagged array is an arrays. You can declare a jagged array named
scores of type int as:
int [][] scores;

C# - Arrays
Jagged Arrays
Declaring an array, does not create the array in memory. To create
the above array:
int[][] scores = new int[5][];
for (int i = 0; i < scores.Length; i++)
{
scores[i] = new int[4];
}

C# - Arrays
Jagged Arrays
You can initialize a jagged array as:
Where, scores is an array of two arrays of integers – scores[0] is an
array of 3 integers and scores[1] is an array of 4 integers.
int[][] scores = new int[2][]{new int[]{92,93,94},new int[]{85,66,87,88}};

C# - Arrays
Passing Arrays as Function Arguments
You can pass an array as a function argument in C#.

C# - Arrays
Param Array
At times, while declaring a method, you are not sure of the number
of arguments passed as a parameter. C# param arrays (or parameter
arrays) come into help at such times.

C# - Arrays
Array Class
The Array class is the base class for all the arrays in C#. It is defined in
the System namespace. The Array class provides various properties
and methods to work with arrays.

C# - Arrays
Properties of the
Array Class
The following table
describes some of the
most commonly used
properties of the
Array class:

C# - Arrays
Methods of the Array
Class
The following table
describes some of the
most commonly used
methods of the Array
class:

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