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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);
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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)
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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
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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
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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)
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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);
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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:
[= ];
int height = 200;
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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
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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;
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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);
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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
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Reading Numbers from the
Console - Example
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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, a*b);
float f = float.Parse(Console.ReadLine());
Console.WriteLine (a, b, f, a*b/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);
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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);
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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);
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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 = x*y; Console.WriteLine("x*y: {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);
}
}
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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";
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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);
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What Is a Variable?\' for single quote \" for double quote
? \\ for backslash \n for new line
? \uXXXX for denoting any other Unicode symbol
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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
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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
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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);
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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.