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CSharp data types

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C# data types

In this part of the C# tutorial, we will talk about data types.
Computer programs work with data. Spreadsheets, text editors, calculators or chat clients. Tools to work with various data types are essential part of a modern computer language. A data type is a set of values, and the allowable operations on those values.
The two fundamental data types in C# are value types and reference types. Primitive types (except strings), enumerations, and structures are value types. Classes, strings, interfaces, arrays, and delegates are reference types. Every type has a default value. Reference types are created on the Heap. The lifetime of the reference type is managed by the .NET framework. The default value for reference types is null reference. Assignment to a variable of a reference type creates a copy of the reference rather than a copy of the referenced value. Value types are created on the stack. The lifetime is determined by the lifetime of the variable. Assignment to a variable of a value type creates a copy of the value being assigned. Value types have different default values. For example, boolean default value is false, decimal 0, string an empty string "".

Boolean values

There is a duality built in our world. There is a Heaven and Earth, water and fire, jing and jang, man and woman, love and hatred. In C# the bool data type is a primitive data type having one of two values: true or false. This is a fundamental data type. Very common in computer programs.
Happy parents are waiting a child to be born. They have chosen a name for both possibilities. If it is going to be a boy, they have chosen John. If it is going to be a girl, they have chosen Victoria. 
using System;

class CSharpApp
{
    static void Main()
    {
        bool male = false;

        Random random = new Random();
        male = Convert.ToBoolean(random.Next(0, 2));

        if (male) {
            Console.WriteLine("We will use name John");
        } else {
            Console.WriteLine("We will use name Victoria");
        }
    }
}
The program uses a random number generator to simulate our case. 
bool male = false;
The male variable is our boolean variable, initiated at first to false. 
Random random = new Random();
We create a Random object, which is used to compute random numbers. It is part of the System namespace. 
male = Convert.ToBoolean(random.Next(0, 2));
The Next() method returns a random number within a specified range. The lower bound is included, the upper bound is not. In other words, we receive either 0, or 1. Later the Convert()method converts these values to boolean ones. 0 to false, 1 to true. 
if (male) {
    Console.WriteLine("We will use name John");
} else {
    Console.WriteLine("We will use name Victoria");
}
If the male variable is set to true, we choose name John. Otherwise, we choose name Victoria. Control structures like if/else statements work with boolean values. 
$ ./kid.exe 
We will use name Victoria
$ ./kid.exe 
We will use name John
$ ./kid.exe 
We will use name John
Running the program several times.

Integers

Integers are a subset of the real numbers. They are written without a fraction or a decimal component. Integers fall within a set Z = {..., -2, -1, 0, 1, 2, ...} Integers are infinite.
In computer languages, integers are primitive data types. Computers can practically work only with a subset of integer values, because computers have finite capacity. Integers are used to count discrete entities. We can have 3, 4, 6 humans, but we cannot have 3.33 humans. We can have 3.33 kilograms.
VB Alias.NET TypeSizeRange
sbyteSystem.SByte1 byte -128 to 127
byteSystem.Byte1 byte0 to 255
shortSystem.Int16 2 bytes-32,768 to 32,767
ushortSystem.UInt162 bytes0 to 65,535
intSystem.Int324 bytes-2,147,483,648 to 2,147,483,647
uintSystem.UInt324 bytes0 to 4,294,967,295
longSystem.Int648 bytes-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulongSystem.UInt648 bytes 0 to 18,446,744,073,709,551,615
These integer types may be used according to our needs. No one, (except perhaps for some biblical people), can be older than 120, 130 years. We can then use the byte type for age variable in a program. This will save some memory. 
using System;

class CSharpApp
{
    static void Main()
    {        
        byte a = 254;
        
        Console.WriteLine(a);
        a++;
        Console.WriteLine(a);
        a++;
        Console.WriteLine(a);
        a++;
        Console.WriteLine(a);
    }
}
In this example, we try to assign a value beyond the range of a data type. This leads to an arithmetic overflow. An arithmetic overflow is a condition that occurs when a calculation produces a result that is greater in magnitude than that which a given register or storage location can store or represent. 
$ ./overflow.exe 
254
255
0
1
In C#, when an overflow occurs, the variable is reset to zero. In contrast, Visual Basic would throw an exception.
Notations Integers can be specified in two different notations in C#. Decimal and hexadecimal. There are no notations for octal or binary values. Decimal numbers are used normally, as we know them. Hexadecimal numbers are preceded with 0x characters. 
using System;

class CSharpApp
{
    static void Main()
    {        
        int num1 = 31;
        int num2 = 0x31;
        
        Console.WriteLine(num1);
        Console.WriteLine(num2);
    }
}
We assign 31 to two variables using two different notations. And we print them to the console. 
$ ./intnotations.exe 
31
49
The default notation is the decimal. The program shows these two numbers in decimal. In other words, hexadecimal 0x31 is 49 decimal.
Counting apples If we work with integers, we deal with discrete entities. We would use integers to count apples. 
using System;

class CSharpApp
{
    static void Main()
    {

        // number of baskets
        int baskets = 16;

        // number of apples in each basket 
        int apples_in_basket = 24;

        // total number of apples
        int total = baskets * apples_in_basket;

        Console.WriteLine("There are total of {0} apples", total);
        
    }
}
In our program, we count the total amount of apples. We use the multiplication operation. 
$ ./apples.exe 
There are total of 384 apples

The output of the program.

Floating point numbers

Floating point numbers represent real numbers in computing. Real numbers measure continuous quantities. Like weight, height or speed. In C# we have three floating point types: float, double and decimal.
C# Alias.NET TypeSizePrecisionRange
floatSystem.Single 4 bytes7 digits1.5 x 10-45 to 3.4 x 1038
doubleSystem.Double8 bytes 15-16 digits5.0 x 10-324 to 1.7 x 10308
decimalSystem.Decimal16 bytes28-29 decimal places 1.0 x 10-28 to 7.9 x 1028
The above table gives the characteristics of the floating point types.
By default, real numbers are double in C# programs. To use a different type, we must use a suffix. The F/f for float numbers and M/m for decimal numbers. 
using System;

class CSharpApp
{
    static void Main()
    {
        float   n1 = 1.234f;
        double  n2 = 1.234;
        decimal n3 = 1.234m;

        Console.WriteLine(n1);
        Console.WriteLine(n2);
        Console.WriteLine(n3);

        Console.WriteLine(n1.GetType());
        Console.WriteLine(n2.GetType());
        Console.WriteLine(n3.GetType());
    }
}
In the above program, we use three different literal notations for floating point numbers. 
float   n1 = 1.234f;
The f suffix is used for a float number. 
double  n2 = 1.234;
If we don't use a suffix, then it is a double number. 
Console.WriteLine(n1.GetType());
The GetType() method returns the type of the number. 
$ ./floats.exe
1.234
1.234
1.234
System.Single
System.Double
System.Decimal
Output.
We can use various syntax to create floating point values. 
using System;

class CSharpApp
{
    static void Main()
    {
        float n1 = 1.234f;
        float n2 = 1.2e-3f;
        float n3 = (float) 1 / 3;

        Console.WriteLine(n1);
        Console.WriteLine(n2);
        Console.WriteLine(n3);
    }
}
We have three ways to create floating point values. The first is the 'normal' way using a decimal point. The second uses scientific notation. And the last one as a result of a numerical operation. 
float n2 = 1.2e-3f;
This is the scientific notation for floating point numbers. Also known as exponential notation, it is a way of writing numbers too large or small to be conveniently written in standard decimal notation. 
float n3 = (float) 1 / 3;
The (float) construct is called casting. The division operation returns integer numbers by default. By casting we get a float number. 
$ ./fnotations.exe 
1.234
0.0012
0.3333333
This is the output of the above program. 
using System;

class CSharpApp
{
    static void Main()
    {
        float  n1 = (float) 1 / 3;
        double n2 = (double) 1 / 3;

        if (n1 == n2) 
        {
            Console.WriteLine("Numbers are equal");
        } else {
            Console.WriteLine("Numbers are not equal");
        }
    }
}
The float and double values are stored with different precision. Caution should be exercised when comparing floating point values. 
$ ./fequal.exe 
Numbers are not equal
And the numbers are not equal.
Let's say a sprinter for 100m ran 9.87s. What is his speed in km/h? 
using System;

class CSharpApp
{
    static void Main()
    {
        float distance;
        float time;
        float speed;
        
        // 100m is 0.1 km

        distance = 0.1f;

        // 9.87s is 9.87/60*60 h

        time = 9.87f / 3600;

        speed = distance / time;

        Console.WriteLine("The average speed of a sprinter is {0} km/h", speed);
    }
}
In this example, it is necessary to use floating point values. 
speed = distance / time;
To get the speed, we divide the distance by the time. 
$ ./sprinter.exe 
The average speed of a sprinter is 36.47416 km/h
This is the output of the sprinter program.

Enumerations

Enumerated type (also called enumeration or enum) is a data type consisting of a set of named values. A variable that has been declared as having an enumerated type can be assigned any of the enumerators as a value. Enumerations make the code more readable. 
using System;

class CSharpApp
{
    enum Days 
    {
        Monday,
        Tuesday,
        Wednesday,
        Thursday,
        Friday,
        Saturday,
        Sunday
    }

    static void Main()
    {

        Days day = Days.Monday;
        
        if (day == Days.Monday)
        {
            Console.WriteLine("It is Monday");
        }

        Console.WriteLine(day);

        foreach(int i in Enum.GetValues(typeof(Days)))
            Console.WriteLine(i);
    }
}
In our code example, we create an enumeration for week days. 
enum Days 
{
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday
}
The enumeration is created with a enum keyword. The Monday, Tuesday ... barewords store in fact numbers 0..6. 
Days day = Days.Monday;
We have a variable called day, which is of enumerated type Days. It is initialized to Monday. 
if (day == Days.Monday)
{
    Console.WriteLine("It is Monday");
}
This code is more readable than if comparing a day variable to some number. 
Console.WriteLine(day);
This line prints Monday to the console. 
foreach(int i in Enum.GetValues(typeof(Days)))
    Console.WriteLine(i);
This loop prints 0..6 to the console. We get underlying types of the enum values. For a computer, an enum is just a number. The typeof is an operator used to obtain the System.Type object for a type. It is needed by the GetValues() method. This method returns an array of the values of in a specified enumeration. And the foreach keyword goes through the array, element by element and prints them to the terminal.
We further work with enumerations. 
using System;

class CSharpApp
{
    public enum Seasons : byte
    {
        Spring = 1,
        Summer = 2,
        Autumn = 3,
        Winter = 4
    }

    static void Main()
    {
        Seasons s1 = Seasons.Spring;
        Seasons s2 = Seasons.Autumn;
        
        Console.WriteLine(s1);
        Console.WriteLine(s2);
    }
}
Seasons can be easily used as enums. We can specify the underlying type for the enum plus we can give exact values for them. 
public enum Seasons : byte
{
    Spring = 1,
    Summer = 2,
    Autumn = 3,
    Winter = 4
}
With a colon and a data type we specify the underlying type for the enum. We also give each member a specific number. 
Console.WriteLine(s1);
Console.WriteLine(s2);
These two lines print the enum values to the console. 
$ ./seasons.exe 
Spring
Autumn
Output.

Strings and chars

string is a data type representing textual data in computer programs. A string in C# is a sequence of unicode characters. A charis a single unicode character. Strings are enclosed by double quotes.
Since strings are very important in every programming language, we will dedicate a whole chapter to them. Here we only drop a small example. 
using System;

class CSharpApp
{
    static void Main()
    {
        string word = "ZetCode";

        char c = word[0];

        Console.WriteLine(c);
    }
}
The program prints Z character to the terminal. 
string word = "ZetCode";
Here we create a string variable and assign it "ZetCode" value. 
char c = word[0];
A string is an array of unicode characters. We can use the array access notation to get a specific character from the string. The number inside the square brackets is the index into the array of characters. The index is counted from zero. That means, the first character has index 0. 
$ ./char.exe 
Z
The program prints the first character of the "ZetCode" string to the console.

Arrays

Array is a complex data type which handles a collection of elements. Each of the elements can be accessed by an index. All the elements of an array must be of the same data type.
We dedicate a whole chapter to arrays, here we show only a small example. 
using System;

class CSharpApp
{
    static void Main()
    {
        
        int[] numbers = new int[5];

        numbers[0] = 3;
        numbers[1] = 2;
        numbers[2] = 1;
        numbers[3] = 5;
        numbers[4] = 6;

        int len = numbers.Length;

        for (int i=0; i<len; i++) 
        {
            Console.WriteLine(numbers[i]);
        }
    }
}
In this example, we declare an array, fill it with data and then print the contents of the array to the console. 
int[] numbers = new int[5];
We declare an integer array, which can store up to 5 integers. So we have an array of five elements, with indexes 0..4. 
numbers[0] = 3;
numbers[1] = 2;
numbers[2] = 1;
numbers[3] = 5;
numbers[4] = 6;
Here we assign values to the created array. We can access the elements of an array by the array access notation. It consists of the array name followed by square brackets. Inside the brackets we specify the index to the element, we want. 
int len = numbers.Length;
Each array has a Length property, which returns the number of elements in the array. 
for (int i=0; i<len; i++) 
{
    Console.WriteLine(numbers[i]);
}
We traverse the array and print the data to the console.

DateTime

The DateTime is value type. It represents an instant in time, typically expressed as a date and time of day. 
using System;

class CSharpApp
{
    static void Main()
    {
        DateTime today;

        today = DateTime.Now;

        System.Console.WriteLine(today);
        System.Console.WriteLine(today.ToShortDateString());
        System.Console.WriteLine(today.ToShortTimeString());               

    }
}
We show today's date in three different formats. Date & time, date and time. 
DateTime today;
We declare a variable of DateTime data type. 
today = DateTime.Now;
Gets a DateTime object that is set to the current date and time on this computer, expressed as the local time. 
System.Console.WriteLine(today);
This line prints the date in full format. 
System.Console.WriteLine(today.ToShortDateString());
System.Console.WriteLine(today.ToShortTimeString());
The ToShortDateString()returns a short date string format, the ToShortTimeString()returns a short time string format. 
$ ./date.exe 
10/15/2010 10:56:37 AM
10/15/2010
10:56 AM
The output of the example.

Type casting

We often work with multiple data types at once. Converting one data type to another one is a common job in programming. Type conversion or typecasting refers to changing an entity of one data type into another. There are two types of conversion. Implicit and explicit. Implicit type conversion, also known as coercion, is an automatic type conversion by the compiler. 
using System;

class CSharpApp
{
    static void Main()
    {

        int  val1 = 0;
        byte val2 = 15;

        val1 = val2;         

        Console.WriteLine(val1.GetType());
        Console.WriteLine(val2.GetType());

        Console.WriteLine(12 + 12.5);
        Console.WriteLine("12" + 12);

    }
}
In this example, we have several implicit conversions. 
val1 = val2;
Here we work with two different types. int and byte. We assign a byte value to an int value. It is a widening operation. int values have four bytes, byte values have only one byte. Widening conversions are allowed. If we wanted to assign a intto a byte, this would be a shortening conversion. Implicit shortening conversions are not allowed by C# compiler. This is because in implicit shortening conversion we could unintentionally loose precision. We can do shortening conversions, but we must inform the compiler about it. That we know what we are doing. It can be done with explicit conversion. 
Console.WriteLine(12 + 12.5);
We add two values. One integer and one floating point value. The result is a floating point value. It is a widening implicit conversion. 
Console.WriteLine("12" + 12);
The result is 1212. An integer is converted to a string and the two strings are concatenated.
> Next we will show some explicit conversions in C#. 
using System;

class CSharpApp
{
    static void Main()
    {
        float a;
        double b = 13.5;
        int c;
        
        a = (float) b;
        c = (int) a;

        Console.WriteLine(a);
        Console.WriteLine(b);
        Console.WriteLine(c);
    }
}
We have three values. We do some explicit conversions with these values. 
float a;
double b = 13.5;
int c;
We have a float value a double value and a int value. 
a = (float) b;
We convert a double value to a floatvalue. Explicit conversion is done by specifying the intended type between two square brackets. In this case, no precision is lost. 13.5 can be safely assigned to both types. 
c = (int) a;
We convert a float value to int value. In this statement, we loose some precision. 13.5 becomes 13. 
$ ./explicit.exe 
13.5
13.5
13
Output of the example.

Nullable types

Value types cannot be assigned a null literal. Reference types can. Applications that work with databases deal with the null value. Because of this, special nullable types were introduced into the C# language. Nullable types are instances of the System.Nullable<T> struct. 
using System;

class CSharpApp
{
    static void Main()
    {
        Nullable<bool> male = null;
        int? age = null;

        Console.WriteLine(male.HasValue);
        Console.WriteLine(age.HasValue);
    }
}
A simple example demonstrating nullable types. 
Nullable<bool> male = null;
int? age = null;
There are two ways how to declare a nullable type. Either with the Nullable<T> generic structure, in which the type is specified between the angle brackets. Or we can use a question mark after the type. The latter is in fact a shorthand for the first notation. 
$ ./nullabletypes.exe 
False
False
Output.

Convert & Parse methods

There are two groups of methods, which aid us at converting values. 
using System;

class CSharpApp
{
    static void Main()
    {
        Console.WriteLine(Convert.ToBoolean(0.3));
        Console.WriteLine(Convert.ToBoolean(3));
        Console.WriteLine(Convert.ToBoolean(0));
        Console.WriteLine(Convert.ToBoolean(-1));

        Console.WriteLine(Convert.ToInt32("452"));
        Console.WriteLine(Convert.ToInt32(34.5));
    }
}
The Convert class has many methods for converting values. We use two of them. 
Console.WriteLine(Convert.ToBoolean(0.3));
We convert a double value to a bool value. 
Console.WriteLine(Convert.ToInt32("452"));
And here we convert a string to int. 
using System;

class CSharpApp
{
    static void Main()
    {
        Console.WriteLine(Int32.Parse("34"));
        Console.WriteLine(Int32.Parse("-34"));
        Console.WriteLine(Int32.Parse("+34"));
    }
}
Converting strings to integers is a very common task. Often when we bring values from databases or GUI widgets. 
Console.WriteLine(Int32.Parse("34"));
We use the Parse() method of the Int32 class to convert a string to int value.
In this part of the C# tutorial, we covered data types and their conversions.

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