.NET C# Guide

Variables

Examples of declaring several variables are here. There are six variables declared and four of them are initialized using the assignment operator (=).

int i = 123, x;
int j;
double d = 1.1;
char ch = 'A';
float f = 1f;

Variables can also be initialized with other variables.

int i = 123;
int j = i + 10; // j contains 133
int x = i; // x contains 123

Nullable Variables

Some variables cannot normally be assigned the value of null, such as numbers and bool variables. To allow null to be assigned to these variables then use ?.

int? i = null;
double? d = null;
float? f = null;
bool? b = null; // effectively becomes a tri-state variable with the addition of null

Operators

Operators are symbols that tell the compiler to perform a specific mathematical or logical manipulation. Basically, C# has four classes of operators: arithmetic, bitwise, relational and logical.

Arithmetic Operators

operator	operation
+	addition
-	subtraction
*	multiplication
/	division
%	modulus
++	increment
--	decrement

The operators +, -, *, and / all work as expected. The % operator (modulus) returns the remainder of an integer division. Interestingly, it also works with floating-point types which is something that C/C++ cannot do.

Increment and Decrement

The operators -- and ++ decrement and increment by one, respectively. They come in two flavors: prefix and postfix. These operators only work on variables. The prefix one works as one would expect.

int num = 10;
int i;
i = ++num + 10; // i is 21, num is 11
i = --num + 10; // i is 20, num is 10

The postfix increment/decrement operators are not so obvious.

int num = 10;
int i;
i = num++ + 10; // i is 20, num is 11
i = num-- + 10; // i is 21, num is 10

The Assignment Operator: =

Consider this example:

int a, b, c;
a = b = c = 10; // a, b, and c equal 10

int x, y, z = 3; // z equals 3
x = y = z; // x and y equal 3

z = z + 6; // z equals 9

The statement a = b = c = 10; is an example of a chain of assignments.

Compound Assignments

Compound assignments simplify the coding of some assignment statments. Consider this example:

int i = 0;
i = i + 5; // i equals 5
i += 10; // i equals 15

The arithmetic and logical assignment operators are: += += *= /= &= %= ^= |=

Relational Operators

operator	operation
==	equal to
!=	not equal to
>	greater than
<	less than
>=	greater than or equal
<=	less than or equal

Logical Operators

operator	operation
&	AND
\|	OR
^	XOR
!	NOT
\|\|	short-circuit OR
&&	short-circuit AND

Short-circuit Operators

Short-circuit AND and short-circuit OR operators are special AND and OR operators. The only difference between the short-circuit and normal versions is that the short-circuit version will evaluate the second operand only when necessary while the normal version always evaluates the second operand.

Bitwise Operators

operator	operation
&	AND
\|	OR
^	XOR
<<	shift left
>>	shift right
~	unary NOT

The Conditional Operator: ?

The ? is a ternary operator because it requires three operands. It's syntax is: expression1 ? expression2 : expression3 where expression1 is a bool and if true then the entire statement evaluates to expression2 otherwise it's expression3.

int x = 0, i = 10;
i = (x == 0) ? i : (i / x);

The Coalescing Operator: ??

The coalescing operator uses the syntax ?? to define a default value for the conversion in case the nullable type has a value of null. Here, str2 receives a value of string.Empty because str1 is null.

string str1 = null;
string str2 = str1 ?? string.Empty;

The operators of C# are almost identical to the JavaScript ones with the exception of >>>, ===, and !== as C# does not have these. And, values of Infinity and NaN do not exist in C#. Note that JavaScript only supports a few data types unlike C#. The C# operators are identical to the C/C++ ones.

Example Program Code

This example uses the short-circuit AND to prevent the numerator from being divided by the denominator which is set to zero.

using System;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main(string[] args)
		{
			int numerator = 100;
			int denominator = 0; // CANNOT DIVIDE BY ZERO!!!

			// first check that denominator is "not equal to" zero
			// if it is not then divide numerator by denominator
			if ((denominator != 0) && ((numerator / denominator) == 1))
				Console.WriteLine("numerator and denominator are equal.");
			else
				Console.WriteLine("numerator and denominator are not equal.");
		}
	}
}

This example uses the normal AND which will not prevent the numerator from being divided by the denominator which is set to zero. This will result in a divide-by-zero error which will crash the program.

using System;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main(string[] args)
		{
			int numerator = 100;
			int denominator = 0; // CANNOT DIVIDE BY ZERO!!!

			// first check that denominator is "not equal to" zero
			// but also evaluate the second operand thereby dividing
			// the numerator by the denominator crashing the program
			if ((denominator != 0) & ((numerator / denominator) == 1))
				Console.WriteLine("numerator and denominator are equal.");
			else
				Console.WriteLine("numerator and denominator are not equal.");
		}
	}
}

Operator Precedence

Highest Precedence
() [] . ++(postfix) --(postfix) checked	new sizeof typeof unchecked
!	~	(cast)		+(unary)	-(unary) ++(prefix) --(prefix)
* / %
+ -
<< >>
< > <= >= is
== !=
&
^
|
&&
||
?:
= += -= *= /= %= &= |= ^=
Lowest Precedence

Parentheses

Just like in algebra, parentheses increase the precendence of the operations contained with in them.

int i = 20 / 2 * 5; // i equals 50

int j = 20 / (2 * 5); // j equals 2

Type Casting

Casting instructs the compiler to convert one type into another. Put the cast inside parentheses as follows.

double d = 1000.1;

int i = (int)d; // (int) is the cast; now i equals 1000

byte b = (byte)i; // b cannot fit 1000 so data is lost (b equals 232 because 2 bits were lost)

Also, casting can be done at runtime using the as keyword. If the cast succeeds then a reference to type is returned otherwise null is returned.

Type Identification

It is possible to determine an object's type at runtime using the keywords is and typeof.

To determine if an object is a certain type use the is operator.

using System;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main(string[] args)
		{
			string s = string.Empty;
			object o = s;
			int[] n = { 1, 2, 3 };

			if (s is string)
				Console.WriteLine("s is a string");
			else
				Console.WriteLine("s is not a string");

			if (s is object)
				Console.WriteLine("s is an object");
			else
				Console.WriteLine("s is not an object");

			if (o is string)
				Console.WriteLine("o is a string");
			else
				Console.WriteLine("o is not a string");

			if (o is object)
				Console.WriteLine("o is an object");
			else
				Console.WriteLine("o is not an object");

			if (n is string)
				Console.WriteLine("n is a string");
			else
				Console.WriteLine("n is not a string");

			if (n is object)
				Console.WriteLine("n is an object");
			else
				Console.WriteLine("n is not an object");

			if (n is Array)
				Console.WriteLine("n is an Array");
			else
				Console.WriteLine("n is not an Array");

		}
	}
}

Using typeof:

using System;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main(string[] args)
		{
			Type t;

			t = typeof(Console);
			Console.WriteLine(t.FullName);

			t = typeof(Program);
			Console.WriteLine(t.FullName);
		}
	}
}

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