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Introduction to computer systems CSC 115 Primitive Data Types and Variables How Computing Works?Console.WriteLine("a+b={0} sum={1} equal={2}", a+b, sum, equal); 41 Decimal Floating-Point Types ? There is a special decimal floating-point real number type in C#: ? decimal (+-1,0 x 10-28 to +-7,9 x 1028): 128-bits, precision of 28-29 digits ? Used for financial calculations ? No round-off errors ? Almost no loss of precision ? The default value of decimal type is: ? 0.0M (M is the suffix for decimal numbers) 42 The Boolean Data Type ? The Boolean data type: ? Is declared by the bool keyword ? Has two possible values: true and false ? Is useful in logical expressions ? The default value is false 43 Boolean Values - Example ? Example of boolean variables taking values of true or false: int a = 1; int b = 2; bool greaterAB = (a > b); Console.WriteLine(greaterAB); // False bool equalA1 = (a == 1); Console.WriteLine(equalA1); // True 44 The Character Data Type ? The character data type: ? Represents symbolic information ? Is declared by the char keyword ? Gives each symbol a corresponding integer code ? Has a '\0' default value ? Takes 16 bits of memory (from U+0000 to U+FFFF) 45 Characters and Codes ? The example below shows that every symbol has an its unique Unicode code: char symbol = 'a'; Console.WriteLine("The code of '{0}' is: {1}", symbol, (int) symbol); symbol = 'b'; Console.WriteLine("The code of '{0}' is: {1}", symbol, (int) symbol); symbol = 'A'; Console.WriteLine("The code of '{0}' is: {1}", symbol, (int) symbol); 46 The String Data Type ?class_"A"? point9 ? Declaring Variables ? When declaring a variable we: ? Specify its type ? Specify its name (called identifier) ? May give it an initial value ? The syntax is the following: ? Example: <data_type> [= ]; int height = 200; 53 Initializing Variables ? Initializing ? Is assigning of initial value ? Must be done before the variable is used! ? Several ways of initializing: ? By using the new keyword ? By using a literal expression ? By referring to an already initialized variable 54 Initialization - Examples ? Example of some initializations: // The following would assign the default // value of the int type to num: int num = new int(); // num = 0 // This is how we use a literal expression: float heightInMeters = 1.74f; // Here we use an already initialized variable: string greeting = "Hello World!"; string message = greeting; 55 Escaping Sequences ?Using a Structure Type Employee companyEmployee; companyEmployee.firstName = "Joe"; companyEmployee.age = 23; public struct Employee { public string firstName; public int age; } Thinking Corner: Ants ? An ant starts walking on a bright whose length is m meters. The ant walks with velocity v meters/second. After arriving at one end of the bridge, it walks back with the same speed. It keeps walking for t minutes. How many rounds that the ant completely crosses the bridge and gets back to the starting point? Write a program that takes m, v, and t , as double, and compute how many rounds that the ant walks over the bridge. Ideas ? From the duration and speed, we can calculate the total distance the ant walks. ? From the distance and the length of the bridge, we can calculate the number of rounds ? The problem we have to solve is that how we manage to removes all the fractions in the result by the division. ? We will start with a program that compute the number of rounds, in real, and we will fix this problem later. Partial solution ? method Main static void Main() { Console.Write("Enter m (m): "); double m = double.Parse(Console.ReadLine()); Console.Write("Enter v (m/s): "); double v = double.Parse(Console.ReadLine()); Console.Write("Enter t (min): "); double t = double.Parse(Console.ReadLine()); double dist = v * t * 60; (click to show) Can You Spot the Disallowed Variable Names?int.Parse(string) - parses a string to int string str = Console.ReadLine() int number = int.Parse(str); Console.WriteLine("You entered: ", number); 15 Converting Strings to Numbers ? Numeral types have a method Parse(...) for extracting the numeral value from a string ? int.Parse(string) - string -> int ? long.Parse(string) - string -> long ? float.Parse(string) - string -> float ? Causes FormatException in case of error string s = "123"; int i = int.Parse(s); // i = 123 long l = long.Parse(s); // l = 123L string invalid = "xxx1845"; int value = int.Parse(invalid); // FormatException 16 Reading Numbers from the Console - Example 17 static void Main() { int a = int.Parse(Console.ReadLine()); int b = int.Parse(Console.ReadLine()); Console.WriteLine(a, b, a+b); Console.WriteLine(a, b, ab); float f = float.Parse(Console.ReadLine()); Console.WriteLine (a, b, f, ab/f); } Declaring Local Variables ?Depending on the unit of measure we may use different data types: byte centuries = 20; // Usually a small number ushort years = 2000; uint days = 730480; ulong hours = 17531520; // May be a very big number Console.WriteLine("centuries is years, or days, or hours.", centuries, years, days, hours); 13 Console.ReadLine() ? Gets a line of characters ? Returns a string value ? Returns null if the end of the input is reached Console.Write("Please enter your first name: "); string firstName = Console.ReadLine(); Console.Write("Please enter your last name: "); string lastName = Console.ReadLine(); Console.WriteLine("Hello, ",firstName, lastName); 14 Reading Numeral Types ?Specifying extra formatting: Console.WriteLine("Size {0}x{1}", width, height); double salary=12000; Console.WriteLine("My salary is {0:f2}.", salary); Console.WriteLine("Hello"); Console.WriteLine(area); 25 Exercise : Find the output of the following Code ? using System; class Binary { public static void Main() { int x, y, result; float floatresult; x = 7; y = 5; result = x+y; Console.WriteLine("x+y: {0}", result); result = x-y; Console.WriteLine("x-y: {0}", result); result = xy; Console.WriteLine("xy: {0}", result); result = x/y; Console.WriteLine("x/y: {0}", result); floatresult = (float)x/(float)y; Console.WriteLine("x/y: {0}", floatresult); result = x%y; Console.WriteLine("x%y: {0}", result); result += x; Console.WriteLine("result+=x: {0}", result); } } 26 And here's the output: x+y: 12 x-y: 2 x*y: 35 x/y: 1 x/y: 1.4 x%y: 2 ?Using the + operator string s = "Microsoft .NET Framework"; 47 Saying Hello - Example ? Concatenating the two names of a person to obtain his full name: ? NOTE: a space is missing between the two names! We have to add it manually string firstName = "Ivan"; string lastName = "Ivanov"; Console.WriteLine("Hello, {0}!\n", firstName); string fullName = firstName + " " + lastName; Console.WriteLine("Your full name is {0}.", fullName); 48 What Is a Variable?' for single quote " for double quote ? \ for backslash \n for new line ? \uXXXX for denoting any other Unicode symbol 56 Character Literals - Example ? Examples of different character literals: char symbol = 'a'; // An ordinary symbol symbol = '\u006F'; // Unicode symbol code in // a hexadecimal format symbol = '\u8449'; // ? (Leaf in Traditional Chinese) symbol = '''; // Assigning the single quote symbol symbol = '\'; // Assigning the backslash symbol symbol = '\n'; // Assigning new line symbol symbol = '\t'; // Assigning TAB symbol symbol = "a"; // Incorrect: use single quotes 57 Structure Types ?May lose precision, but not magnitude using System; class Test { static void Main( ) { int intValue = 123; long longValue = intValue; Console.WriteLine("(long) {0} = {1}", intValue, ?longValue); } } Explicit Data Type Conversion ? To do explicit conversions, use a cast expression: using System; class Test { static void Main( ) { long longValue = Int64.MaxValue; int intValue = (int) longValue; Console.WriteLine("(int) {0} = {1}", longValue, ?intValue); } } What are Floating-Point Types?struct User-Defined Value Types Built-in Type Data Types 9 Type Size Description Range bool 1 byte Store truth value true / false char 1 byte Store one character character code 0 - 255 byte 1 byte Store positive integer 0 - 255 short 2 byte Store integer -32,768 -- 32,767 int 4 byte Store integer -2.1 x 109 -- 2.1 x 109 long 8 byte Store integer -9.2 x 1018 -- 9.2 x 1018 double 16 byte Store real number +- 5.0x10-324 -- +- 1.7x10308 string N/A Store sequence of characters N/A What are Integer Types?NOTE: The "f" suffix in the first statement! ? Real numbers are by default interpreted as double! ? One should explicitly convert them to float float floatPI = 3.141592653589793238f; double doublePI = 3.141592653589793238; Console.WriteLine("Float PI is: {0}", floatPI); Console.WriteLine("Double PI is: {0}", doublePI); 40 Floating-Point Calculations ?Declare five variables choosing for each of them the most appropriate of the types byte, sbyte, short, ushort, int, uint, long, ulong to represent the following values: 52130, -115, 4825932, 97, -10000.???????????????2.3.5.6.8.

Introduction to computer systems
CSC 115
Primitive Data
Types and Variables
How Computing Works?
 Computers are machines that process data
 Data is stored in the computer memory in
variables
 Variables have data type, name and value
 Example of variable definition and assignment
in C#
int count = 5;
Data type
Variable name
Variable value
3
What Is a Data Type?
 A data type:
 Is a domain of values of similar characteristics
 Defines the type of information stored in the
computer memory (in a variable)
 Examples:
 Positive integers: 1, 2, 3, …
 Alphabetical characters: a, b, c, …
4
Data Type Characteristics
 A data type has:
 Name (C# keyword ---- int, double)
 Size (how much memory is used)
 Default value
 Example:
 Integer numbers in C#
 Name: int
 Size: 32 bits (4 bytes)
 Default value: zero
5
Overview of Common Type System (CTS
 CTS supports both value and reference types
Reference Type
Type
Value Type
Comparing Value and
Reference Types
◼ Value types:
◼ Directly contain
their data
◼ Each has its own
copy of data
◼ Operations on one
cannot affect
another
◼ Reference types:
◼ Store references to their
data (known as objects)
◼ Two reference variables
can reference same
object
◼ Operations on one can
affect another
Comparing Built-in and UserDefined Value Types
◼ Examples of
built-in value
types:
◼ Int
◼ double
◼ Examples of user-defined
value types:
◼ enum
◼ struct
User-Defined
Value Types
Built-in Type
Data Types
9
Type Size Description Range
bool 1 byte Store truth value true / false
char 1 byte Store one character character code 0 – 255
byte 1 byte Store positive integer 0 – 255
short 2 byte Store integer -32,768 -- 32,767
int 4 byte Store integer -2.1 x 109
-- 2.1 x 109
long 8 byte Store integer -9.2 x 1018
-- 9.2 x 1018
double 16 byte Store real number ± 5.0x10-324
-- ±
1.7x10308
string N/A Store sequence of
characters
N/A
What are Integer Types?
 Integer types:
 Represent whole numbers
 May be signed or unsigned
 Have range of values, depending on the size of
memory used
 The default value of integer types is:
 0 – for integer types, except
 0L – for the long type
10
Integer Types
 Integer types are:
 sbyte (-128 to 127): signed 8-bit
 byte (0 to 255): unsigned 8-bit
 short (-32,768 to 32,767): signed 16-bit
 ushort (0 to 65,535): unsigned 16-bit
 int (-2,147,483,648 to 2,147,483,647): signed
32-bit
 uint (0 to 4,294,967,295): unsigned 32-bit
11
Integer Types (2)
 More integer types:
 long (-9,223,372,036,854,775,808 to
9,223,372,036,854,775,807): signed 64-bit
 ulong (0 to 18,446,744,073,709,551,615):
unsigned 64-bit
12
Measuring Time – Example
 Depending on the unit of measure we may use
different data types:
byte centuries = 20; // Usually a small number
ushort years = 2000;
uint days = 730480;
ulong hours = 17531520; // May be a very big number
Console.WriteLine("centuries is years, or days, or
hours.", centuries, years, days, hours);
13
Console.ReadLine()
 Gets a line of characters
 Returns a string value
 Returns null if the end of the input is reached
Console.Write("Please enter your first name: ");
string firstName = Console.ReadLine();
Console.Write("Please enter your last name: ");
string lastName = Console.ReadLine();
Console.WriteLine("Hello, ",firstName, lastName);
14
Reading Numeral Types
 Numeral types can not be read directly from the
console
 To read a numeral type do the following:

1. Read a string value


2. Convert (parse) it to the required numeral type
    int.Parse(string) – parses a string to int
   string str = Console.ReadLine()
   int number = int.Parse(str);
   Console.WriteLine("You entered: ", number);
   15
   Converting Strings to Numbers
    Numeral types have a method Parse(…) for
   extracting the numeral value from a string
    int.Parse(string) – string → int
    long.Parse(string) – string → long
    float.Parse(string) – string → float
    Causes FormatException in case of error
   string s = "123";
   int i = int.Parse(s); // i = 123
   long l = long.Parse(s); // l = 123L
   string invalid = "xxx1845";
   int value = int.Parse(invalid); // FormatException
   16
   Reading Numbers from the
   Console – Example
   17
   static void Main()
   {
   int a = int.Parse(Console.ReadLine());
   int b = int.Parse(Console.ReadLine());
   Console.WriteLine(a, b, a+b);
   Console.WriteLine(a, b, ab);
   float f = float.Parse(Console.ReadLine());
   Console.WriteLine (a, b, f, ab/f);
   }
   Declaring Local Variables
    Usually declared by data type and
   variable name:
    Possible to declare multiple variables
   in one declaration:
   --or--
   int itemCount;
   int itemCount, employeeNumber;
   int itemCount,
   employeeNumber;
   Assigning Values to Variables
    Assign values to variables that are
   already declared:
    Initialize a variable when you declare
   it:
    You can also initialize character
   values:
   int employeeNumber;
   employeeNumber = 23;
   int employeeNumber = 23;
   Compound Assignment
    Adding a value to a variable is very common
    There is a convenient shorthand
    This shorthand works for all arithmetic
   operators
   itemCount = itemCount + 40;
   itemCount += 40;
   itemCount -= 24;
   Increment and Decrement
    Changing a value by one is very common
    There is a convenient shorthand
    This shorthand exists in two forms
   itemCount += 1;
   itemCount -= 1;
   itemCount++;
   itemCount--;
   ++itemCount;
   --itemCount;
   Operators for variable updates
    As in Python, C# provides data update
   operators
   x = x + 10 x += 10
   y = y * 7 y *= 7
   z = z / 7 z /= 7
   Operators ++, --
    We usually increase or decrease a variable by
   one. In C#, it is very easy to do.
   x = x + 1 x += 1 x++
   x = x - 1 x -= 1 x--
   Examples: printing numbers
   int a = 1;
   while(a