OOP with C# by Dr.hakim

1. Data Types
Lecture 2
Dr. Hakem Beitollahi
Computer Engineering Department
Soran University

2. Objectives of this lecture
 In this chapter you will learn:
 Increment and Decrement (++ and --)
 Assignment Operators
 Basic data types in C#
 Constant values
 Conditional logical operators
Data Types— 2

3. Main Mathematic Operations
Operator Action
+ Addition
- Subtraction
* Multiply
/ Division
% Reminder
++ Increment
-- Decrement
Data Types— 3

4. Increment & decrement (I)
 C/C++/C# includes two useful operators not found in some other
computer languages.
 These are the increment and decrement operators, ++ and - -
 The operator ++ adds 1 to its operand, and − − subtracts 1.
 i++ = i + 1
 i-- = i - 1
 Both the increment and decrement operators may either precede
(prefix) or follow (postfix) the operand
 i = i+1 can be written as i++ or ++i
 i = i -1 can be written as i-- or --i
 Please note: There is, however, a difference between the prefix and
postfix forms when you use these operators in an expression
Data Types— 4

5. Increment & decrement (II)
// Increment and Decrement Operations ++/--
using System;
class Comparison
{
static void Main( string[] args )
{
int a = 10;
int b = 10;
int x, y;
x = a++;
y = ++b;
Console.WriteLine("x = {0}, a ={1}.", x, a);
Console.WriteLine("y = {0}, b ={1}.", y, b);
}// end method Main
} // end class Comparison
x = 10 a = 11
y = 11 b = 11
Data Types— 5

6. Increment & decrement (III)
// Increment and Decrement Operations ++/--
using System;
class Comparison
{
static void Main( string[] args )
{
int a = 10;
int b = 10;
Console.WriteLine(a++);
Console.WriteLine(a);
Console.WriteLine(++b);
Console.WriteLine(b);
}// end method Main
} // end class Comparison
10
11
11
11
Data Types— 6

7. Common Programming Error 1
Attempting to use the increment or
decrement operator on an expression
other than a variable reference is a syntax
error. A variable reference is a variable or
expression that can appear on the left side
of an assignment operation. For example,
writing ++(x + 1) is a syntax error,
because (x + 1) is not a variable
reference
Data Types — 7

8. Assignment Operator
Data Types — 8

9. Assignment Operator (I)
 C# provides several assignment operators for
abbreviating assignment expressions.
 Example:
 c = c + 3;
 c += 3;
 where operator is one of the binary operators +,
-, *, / or %, can be written in the form
 variable operator= expression;
Data Types — 9

10. Assignment Operator (II)
Data Types — 10

11. Common Programming Error 1
Placing a space character between symbols
that compose an arithmetic assignment
operator is a syntax error.
A += 6; True A + = 6; False
Data Types — 11

12. Basic Data Types in C#
Data Types— 12

13. Basic data types in C# (I)
 Programming languages store and
process data in various ways depending
on the type of the data; consequently, all
data read, processed, or written by a
program must have a type
 A data type is used to
 Identify the type of a variable when the
variable is declared
 Identify the type of the return value of a
function (later)
 Identify the type of a parameter expected by
a function (later)
Data Types— 13

14. Basic data types in C# (II)
 There are 7 major data types in C++
 char e.g., ‘a’, ‘c’, ‘@’
 string e.g., “Zagros”
 int e.g., 23, -12, 5, 0, 145678
 float e.g., 54.65, -0.004, 65
 double e.g., 54.65, -0.004, 65
 bool only true and false
 void no value
Data Types— 14

15. Basic data types in C# (III)
Type Range Size (bits)
char U+0000 to U+ffff Unicode 16-bit character
sbyte -128 to 127 Signed 8-bit integer
byte 0 to 255 Unsigned 8-bit integer
short -32,768 to 32,767 Signed 16-bit integer
ushort 0 to 65535 Unsigned 16-bit integer
int -2,147,483,648 to 2,147,483,647 Signed 32-bit integer
uint 0 to 4,294,967,295 Unsigned 32-bit integer
long -9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
Signed 64-bit integer
ulong 0 to 18,446,744,073,709,551,615 Unsigned 64-bit integer
float -3.402823e38 .. 3.402823e38 Signed 32 bits
double -1.79769313486232e308 ..
1.79769313486232e308
Signed 64 bits
decimal -79228162514264337593543950335 ..
79228162514264337593543950335
Signed 128 bits
Data Types— 15

16. Basic data types in C# (IV)
 The general form of a declaration is
 Type variable-list
 Examples
 int I, j, k;
 char ch, a;
 float f, balance;
 double d;
 bool decision;
 string str;
 Variables name
Correct incorrect
Count 3count
test23 hi!there
high_balance high...balance
_name Test?
@count co@nt
 The first character must be a letter
 -an underscore or @
 The subsequent characters must be either letters, digits, or
underscores
Data Types— 16

17. Constants in C#
Data Types— 17

18. Const variables (I)
 Variables of type const may not be changed by your
program
 The compiler is free to place variables of this type into
read-only memory (ROM).
 Example:
 const int a = 10;
Data Types— 18

19. // Constant learning
using System;
class Constant
{
static void Main( string[] args )
{
const int c = 999;
// c = 82; Error becuase c is constant and you cannot change it
// c = 999; Error becuase c is constant and you cannot change it
Console.WriteLine(c);
}// end method Main
} // end class Constant
Data Types— 19

20. Conditional Logical operators
Data Types— 20

21. Conditional Logical operators (I)
 Conditional logical operators are useful when we want to
test multiple conditions.
 There are 3 types of conditional logical operators and
they work the same way as the boolean AND, OR and
NOT operators.
 && - Logical AND
 All the conditions must be true for the whole
expression to be true.
 Example: if (a == 10 && b == 9 && d == 1)
means the if statement is only true when a == 10 and
b == 9 and d == 1.
Data Types— 21

22. expression1 expression2 expression1 && expression2
false false false
false true false
true false false
true true true
Data Types— 22

23. Conditional Logical operators (II)
 || - Conditional logical OR
 The truth of one condition is enough to make
the whole expression true.
 Example: if (a == 10 || b == 9 || d == 1)
means the if statement is true when either
one of a, b or d has the right value.
 ! – Conditional logical NOT (also called
logical negation)
 Reverse the meaning of a condition
 Example: if (!(points > 90))
means if points not bigger than 90.
Data Types— 23

24. expression1 expression2 expression1 || expression2
false false false
false true true
true false true
true true true
Expression !expression
false true
true false
Data Types— 24

25. Data Types — 25
// Conditional logical operator
using System;
class Conditional_logical
{
static void Main( string[] args )
{
int a = 10;
int b = 15;
if ((a == 10) && (b == 15))
Console.WriteLine("Apple");
else
Console.WriteLine("Orange");
if ((a == 10) || (b == 15))
Console.WriteLine("Apple");
else
Console.WriteLine("Orange");
if (!(a > 20))
Console.WriteLine("Apple");
else
Console.WriteLine("Orange");
}// end method Main
} // end class
Apple
Apple
Apple

26. Operator preferences
Operators Preferences
() 1
!,~,--,++ 2
*,/,% 3
+, - 4
<, <=, >=, > 5
==, != 6
&& 7
|| 8
Note: in a+++a*a, the * has preference over ++
Note: in ++a+a*a, the ++ has preference over *
Data Types— 26

27. Common Programming Error Tip
Although 3 < x < 7 is a mathematically correct
condition, it does not evaluate as you might expect in
C#. Use ( 3 < x && x < 7 ) to get the proper
evaluation in C#.
Using operator == for assignment and using operator =
for equality are logic errors.
Use your text editor to search for all occurrences of = in
your program and check that you have the correct
assignment operator or logical operator in each place.
Data Types— 27