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3. 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

4. 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

5. 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

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9. == (test equality) - results true or false = (assignment) 9

10. if (condition 1 ) { One line does no need {} but use them anyway } else if (condition 2 ) { } else { } 10

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12. 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

13. C# Primitives TypePrimitiveUsageRange boolSystem.Booleanbooleantrue, false byteSystem.Byte8 bit integer0 - 255 charSystem.Char16 bit Unicode character/u0000 - /uffff decimalSystem.Decimal128 bit decimal +/-1.0x10-28 to +/-7.9x10+28 precision of 28-29 digits doubleSystem.Double64 bit floating point -1.79769313486232e308 to 1.79769313486232e308 floatSystem.Single32 bit floating point +/-1.5x10-45 to +/-3.4x10+38 precision of 7 digits intSystem.Int3232 bit integer-2,147,483,648 to 2,147,483,647 longSystem.Int6464 bit integer -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 sbyteSystem.SByte8 bit integer-128 to 127 shortSystem.Int1616 bit integer-32,768 to 32,767 stringSystem.String-immutable, specified length uintSystem.UInt3232 bit unsigned integer0 to 4,294,967,295 ulongSystem.UInt6464 bit unsigned integer0 to 18,446,744,073,709,551,615 ushortSystem.UInt1616 bit unsigned integer0 to 65,535 13

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17. Prefix and Postfix Operators 17

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20. string message = (userInputValue == “1”)? “You entered ONE”:”You entered SOMETHING ELSE”; 20

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23. By default int type, can be changed 23

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27.  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

28. // 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

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30. Local variables 30

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34. 3 phases 34

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38. // 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

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40. 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

41.  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

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47.  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.BitConverter System.Convert Int32.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. MSDNMSDN 47

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51. // 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

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54. 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