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Transcript of Values & Variablesendustri.eskisehir.edu.tr › mfidan › BİL255 › icerik › week1b.pdf ·...
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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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Example
int k=0, m;
m = ++k;
Values of m and k will be 1
int k=0, m;
m = k++;
m will be 0 and
k will be 1
int k=5, m, n=2;
m = --k + n;
m will be 6 and
k will be 4
int k=0, m, n=7;
m = k++ + --n;
m will be 6 and
k 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;
i = 2;
j = 3 + i++;
k = 3 + ++i;
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;
•m = k-- + ++i;
•m *= j % 4;
•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 Parenthesis
E Exponent
M Multiplication
D Division
A Addition
S Subtraction
1 + 2 * 3 - 4 / 5 = ?
1 + (2 * 3) – (4 / 5)
6.2
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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 = 0
(integer division)
1 + (2 * 3) – (4 / 5)
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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'
Special characters are represented by using “\” prefix.
'\n' : new line'\t' : tab'\'' : single quote'\\' : 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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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
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HOMEWORK
HW1: Install VS .Net 2015
HW2: Write a program to display user’s complete mailing address.Accept user’s name, city, street, pin and house no.
HW3: Write a program to display student information. AcceptStudent’s name, Roll no, Age, class, and university name and displayit on console.
Advanced Computer Programming