1 values & variables. 2 properties of variables should have a type stores data case sensitive...
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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
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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