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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