Lecture 2

Data Types

Dr. Hakem Beitollahi

Computer Engineering DepartmentSoran University

Lecture 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

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Main Mathematic Operations

Operator Action

+ Addition

- Subtraction

* Multiply

/ Division

% Reminder

++ Increment

-- Decrement

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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

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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

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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

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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

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Assignment Operator

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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;

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Assignment Operator (II)

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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

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Basic Data Types in C#

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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)

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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

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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

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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 The first character must be a letter -an underscore or @ The subsequent characters must be either letters, digits, or

underscores

Correct incorrect

Count 3count

test23 hi!there

high_balance high...balance

_name Test?

@count co@nt

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Constants in C#

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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;

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// Constant learningusing 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

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Conditional Logical operators

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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.

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expression1 expression2 expression1 && expression2

false false false false true false true false false true true true

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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.

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expression1 expression2 expression1 || expression2

false false false false true true true false true true true true

Expression !expression

false true true false

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// Conditional logical operatorusing 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

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 *

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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.

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