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Values & Variables

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Properties of variables

Should have a type Stores data Case sensitive Their names can not start with a

number Reserved keywords can not be

used as variable names

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Keywords

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How to define a variable

int x = 3;

Type

Variable

Value

Semicolon: End of statement

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Ways to define a variable

int nInteger;

string sString; int nInteger = 42;string sString = "This is a

string!"; int nInteger;string sString;... nInteger = 42;

sString = "This is a string!";

Double quotes represents a string

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Necessity to set a value to a variable

string sValueless;MessageBox.Show(sValueless);

Error!

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Variable Types

Simple types Integers Floating point numbers Characters Strings

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Integers short 2 bytes (–32,768 <-> 32,767)

short sval = -12; ushort 2 bytes (0 <-> 65,535)

ushort sval= 12; int 4 bytes (–2,147,483,647 <->

2,147,483,647) int nval = -12500;

uint 4 bytes (0 <-> 4,294,967,295) uint nval = 12500;

long 8 bytes long lVal = -548444101;

ulong 8 bytes Ulong lVal = 548444101

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Floating Point Numbers

float 4 bytes float fVal = -1,2;

double 8 bytes double dVal = -3.565;

decimal 8 bytes decimal dVal = -3456.343;

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Expressions

Expressions are used for performing operations over variables.

Return a value of known type. Two types of expressions

Operators Functions

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Arithmetic operations They need more than one variable. Performs mathematical operations

+ (addition operation) - (subtraction operation) * (multiplication operation) / (division operation) % (modulus operation) ….

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Arithmetic operations Abbreviations

int m = 5;int n = 4;

m = m + n; equals m += n;

In other words in the end of both expressions m will have value of 9 and the value of n will not be changed.

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Increment and decrement operations They operate on one variable ++ is increment operator

i++; i = i + 1; -- is decrement operator

i --; i = i – 1; Prefix and postfix operators will

yield to different results. i.e. “i++” and “++i” are not same.

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Increment and decrement operations ++k The result of the operation is the value of

the operand after it has been incremented. k++ The result of the operation is the value of

the operand before it has been incremented. --k The result of the operation is the value of

the operand after it has been decremented. k-- The result of the operation is the value of

the operand before it has been decremented.

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Exampleint k=0, m;int k=0, m;

m = ++k;m = ++k;

Values of Values of mm and and kk will be 1

int k=0, m;int k=0, m;

m = k++;m = k++;

m m will be 0 andkk will be 1

int k=5, m, n=2;int k=5, m, n=2;

m = --k + n;m = --k + n;

mm will be 6 and will be 6 andkk will be 4 will be 4

int k=0, m, n=7;int k=0, m, n=7;

m = k++ + --n;m = k++ + --n;

mm will be 6 and will be 6 andkk will be 1 and will be 1 and n will be 6

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Exercise

What will be the values of the variables after code piece below is executed?

int i, j, k;int i, j, k;

i = 2;i = 2;j = 3 + i++; j = 3 + i++; k = 3 + ++i; k = 3 + ++i; i *= ++k + j--; i *= ++k + j--; i /= k-- + ++j; i /= k-- + ++j;

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Exercise Assuming that line of codes are

independent, what will be the value of variable m after each line is executed?

int i = 0, j = 6, k = 4 , m = 5;int i = 0, j = 6, k = 4 , m = 5;

•m = k-- + ++i; m = k-- + ++i; •m *= j % 4;m *= j % 4;•m += k++ + (j-- * ++i);m += k++ + (j-- * ++i);

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Order of Operations Rules that defines which procedures

should be performed first.

In C# language some operators have execution privilege over others.

To predict the result of an expression first we should know the order of operations.

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Example PEMDAS phrase may help to remember the

order.

P P ParenthesisParenthesisE E ExponentExponentMM MultiplicationMultiplicationDD Division Division AA AdditionAdditionSS SubtractionSubtraction

P P ParenthesisParenthesisE E ExponentExponentMM MultiplicationMultiplicationDD Division Division AA AdditionAdditionSS SubtractionSubtraction

1 + 2 * 3 - 4 / 5 = ?1 + 2 * 3 - 4 / 5 = ?1 + 2 * 3 - 4 / 5 = ?1 + 2 * 3 - 4 / 5 = ?

1 + (2 * 3) – (4 / 5)1 + (2 * 3) – (4 / 5)1 + (2 * 3) – (4 / 5)1 + (2 * 3) – (4 / 5)

6.26.26.26.2

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Example(result) If we use all numbers in integer type then the

result will be integer(In other words fraction will be removed)

4/5 = 04/5 = 0 (integer division)(integer division)

4/5 = 04/5 = 0 (integer division)(integer division)

1 + (2 * 3) – (4 / 5)1 + (2 * 3) – (4 / 5)1 + (2 * 3) – (4 / 5)1 + (2 * 3) – (4 / 5)

77 77

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Exercise

Different data types may yield different results in same operations.

Write and execute the codes in the next slides.

Explain the difference between results.

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Exercise (continues)

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Exercise (continues)

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Characters

char 1 byte 0-256

'a' 'z' 'A' 'Z' '?' '@' '0' '9''a' 'z' 'A' 'Z' '?' '@' '0' '9'

Special characters are represented bSpecial characters are represented byy using using ““\” \” prefix.prefix.

'\n''\n' : new line : new line'\t''\t' : tab : tab'\'''\'' : single quote : single quote'\\''\\' : backslash : backslash

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Strings (Character Arrays)

Sequence of characters.

Example: “Hello!” “first line\n second line \n third line” “” Empty string

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Strings

“string” Class Unicode – 16 bit Example:

string myString = “Hello!”; Verbatim strings

string myString = @“2.5”” disk”;

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string operations

Appending two strings

Result: “Hello world!”

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string operations

Searching within a string int IndexOf ()

Result: 1

Exercise: Find the usage of LastIndexOf() function and write an example by using this function.

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string operations

Retrieve a substring from a string string Substring()

Result : “llo”

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Exercise

Put your name and surname into two string variables.

Concatenate two strings. Write the result to the console.

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DateTime

C# language has built-in “DateTime” structure to represent date and time values.

We can store “year, month, day, hour, minute, second” values in a DateTime structure.

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Creating a DateTime Object

DateTime dt = new DateTime(year, month, day);

Type

Variable name

Creating a new

object

Initial values

DateTime Fundamentals

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Functions and Properties AddDays, AddMonths, AddYears DateTime.Now DayOfWeek

TimeSpan

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Example

A new DateTime object is created

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Constants Their values can not be changed. They have types. We can use them in expressions bur can

not alter them. Defined by using “const” keyword before

variable type. Their values can be set only during

definition line. const int nVar = 34;

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Example