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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Decisions
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Please enter something and press Enter");
string userInputValue;
userInputValue = Console.ReadLine(); //Reading User input
Console.WriteLine("You entered {0}", userInputValue);
Console.ReadLine(); //WAITING
}
}
}3
If, else if, if
static void Main(string[] args)
{
Console.WriteLine("Please 1 or 2");
string userInputValue;
userInputValue = Console.ReadLine(); //READING USER INPUT
if (userInputValue == "1")
{
Console.WriteLine("You entered ONE");
}
else if (userInputValue == "2")
{
Console.WriteLine("You entered TWO");
}
else
{
Console.WriteLine("You entered SOMETHING ELSE");
}
Console.ReadLine(); //WAITING
}
4
Refactoring using message
static void Main(string[] args)
{
Console.WriteLine("Please 1 or 2");
string userInputValue;
userInputValue = Console.ReadLine(); //READING USER INPUT
string message;
if (userInputValue == "1")
{
message = "You entered ONE";
}
else if (userInputValue == "2")
message = "You entered TWO";
else
{
message = "You entered SOMETHING ELSE";
}
Console.WriteLine(message);
Console.ReadLine(); //WAITING
}
5
No {} Only if it is 1 line of code, but not recommended
if else
if(condition1)
{
One line does no need {} but use them anyway
}
else if(condition2)
{
}
else
{
}
10
String.Format
DateTime dt = new DateTime(2012, 1, 17, 9, 30, 0);
string city = "Chicago";
int temp = -16;
string output = String.Format("At {0} in {1}, the temperature was {2}
degrees.", dt, city, temp);
Console.WriteLine(output);// The example displays the following output:
// At 1/17/2012 9:30:00 AM in Chicago, the temperature was -16 degrees.
12
Primitives (again)C# Primitives
Type Primitive Usage Range
bool System.Boolean boolean true, false
byte System.Byte 8 bit integer 0 - 255
char System.Char 16 bit Unicode character /u0000 - /uffff
decimal System.Decimal 128 bit decimal +/-1.0x10-28 to +/-7.9x10+28 precision of
28-29 digits
double System.Double 64 bit floating point -1.79769313486232e308 to
1.79769313486232e308
float System.Single 32 bit floating point +/-1.5x10-45 to +/-3.4x10+38 precision of
7 digits
int System.Int32 32 bit integer -2,147,483,648 to 2,147,483,647
long System.Int64 64 bit integer -9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
sbyte System.SByte 8 bit integer -128 to 127
short System.Int16 16 bit integer -32,768 to 32,767
string System.String - immutable, specified length
uint System.UInt32 32 bit unsigned integer 0 to 4,294,967,295
ulong System.UInt64 64 bit unsigned integer 0 to 18,446,744,073,709,551,615
ushort System.UInt16 16 bit unsigned integer 0 to 65,535
13
Ternary operator example w/ user input (Decisions)
string message =
(userInputValue == “1”)? “You entered ONE”:”You entered SOMETHING ELSE”;
20
Auto-Implemented Properties
In C# 3.0 and later, auto-implemented properties make property-declaration more concise when no additional logic is required in the property accessors.
They also enable client code to create objects. When you declare a property as shown in the following example, the compiler creates a private, anonymous backing field that can only be accessed through the property
No need for getX and setX
27
// This class is mutable. Its data can be modified from outside the class.
class Customer {
// Auto-Implementated Properties for trivial get and set
public double TotalPurchases { get; set; }
public string Name { get; set; }
public int CustomerID { get; set; }
// Constructor
public Customer(double purchases, string name, int ID)
{
TotalPurchases = purchases;
Name = name;
CustomerID = ID;
}
// Methods
public string GetContactInfo() {return "ContactInfo";}
public string GetTransactionHistory() {return "History";}
// .. Additional methods, events, etc.
}
class Program
{
static void Main()
{
// Intialize a new object.
Customer cust1 = new Customer ( 4987.63, "Northwind",90108 );
//Modify a property
cust1.TotalPurchases += 499.99;
}
} 28
// determine the average of an arbitrary number of grades public void DetermineClassAverage() { int total; // sum of grades int gradeCounter; // number of grades entered int grade; // grade value double average; // number with decimal point for average
// initialization phase total = 0; // initialize total gradeCounter = 0; // initialize loop counter
// processing phase // prompt for and read a grade from the user Console.Write( "Enter grade or -1 to quit: " ); grade = Convert.ToInt32( Console.ReadLine() );
// loop until sentinel value is read from the user while ( grade != -1 ) { total = total + grade; // add grade to total gradeCounter = gradeCounter + 1; // increment counter
// prompt for and read the next grade from the user Console.Write( "Enter grade or -1 to quit: " ); grade = Convert.ToInt32( Console.ReadLine() ); } // end while
// termination phase // if the user entered at least one grade... if ( gradeCounter != 0 ) { // calculate the average of all the grades entered average = ( double ) total / gradeCounter;
// display the total and average (with two digits of precision) Console.WriteLine( "\nTotal of the {0} grades entered is {1}", gradeCounter, total ); Console.WriteLine( "Class average is {0:F}", average ); } // end if else // no grades were entered, so output error message Console.WriteLine( "No grades were entered" ); } // end method DetermineClassAverage}
Avoid infinite loop!
38
Explicitly and Implicitly Converting Between Simple Types To perform a floating-point calculation with integer values, we temporarily treat these values as floating-point numbers.
A unary cast operator such as (double) performs explicit conversion.
C# performs an operation called promotion (or implicit conversion) on selected operands for use in the expression.
40
5.9 Formulating Algorithms: Sentinel-Controlled Repetition (Cont..)
The cast operator is formed by placing parentheses around the name of a type. This operator is a unary operator (i.e., an operator that takes only one operand).
Cast operators associate from right to left and have the same precedence as other unary operators, such as unary + and unary -. This precedence is one level higher than that of the multiplicative operators *, / and %.
In this app, the three grades entered during the sample execution of class GradeBookTest (Fig. 5.10) total 263, which yields the average 87.66666….
The format item rounds the average to the hundredths position, and the average is displayed as 87.67.
41
5.9 Formulating Algorithms: Sentinel-Controlled Repetition (Cont..)
Notes Type Conversion
C# statically types at compile time. After variable declaration the type is set
Conversion:◦ Implicit (when it is safe)
From smaller to larger (int to double) From derived to base class
◦ Explicit (cast) Variables compatible, but risk of precision loss (smaller to larger)
◦ Using helpers (between non-compatible types)System.BitConverterSystem.ConvertInt32.Parse
The Convert.ToInt32(String, IFormatProvider) underneath calls the Int32.Parse. So the only difference is that if a null string is passed to Convert it returns 0, whereas Int32.Parse throws an ArgumentNullException. MSDN
47
// Fig. 5.16: Increment.cs
// Prefix increment and postfix increment operators.
using System;
public class Increment
{
public static void Main( string[] args )
{
int c;
// demonstrate postfix increment operator
c = 5; // assign 5 to c
Console.WriteLine( c ); // display 5
Console.WriteLine( c++ ); // display 5 again, then increment
Console.WriteLine( c ); // display 6
Console.WriteLine(); // skip a line
// demonstrate prefix increment operator
c = 5; // assign 5 to c
Console.WriteLine( c ); // display 5
Console.WriteLine( ++c ); // increment then display 6
Console.WriteLine( c ); // display 6 again
} // end Main }
51
5.13 Simple Types (and again)
• The table in Appendix B, Simple Types, lists the 13 simple types in C#.
• C# requires all variables to have a type.
• Instance variables of types char, byte, sbyte, short, ushort, int, uint, long, ulong, float, double, and decimal are all given the value 0 by default.• Instance variables of type bool are given the value false by default.
54