C# Control Statements part 1

1

Reading User Input

2

Code

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

5.5 if Single-Selection Statement

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5.6 if…else Double-Selection Statement

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8

== vs =

== (test equality) - results true or false

= (assignment)

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if else

if(condition1)

{

One line does no need {} but use them anyway

}

else if(condition2)

{

}

else

{

}

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Statement: operators and operands

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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.

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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

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operators

shortcut

14

Comparison operators (return true or false)

15

Logical Operators

16

Increment/Decrement operators

Prefix and Postfix Operators

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Type testing (more later)

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Ternary operator

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Ternary operator example w/ user input (Decisions)

string message =

(userInputValue == “1”)? “You entered ONE”:”You entered SOMETHING ELSE”;

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Operator Precedence

21

Constants

22

Enumerations* (more later)By default int type, can be changed

23

Loops

later

24

5.7 while Repetition Statement

25

5.8 Formulating Algorithms: Counter-Controlled Repetition

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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

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// 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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Local variables

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32

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5.9 Formulating Algorithms: Sentinel-Controlled Repetition

3 phases

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// 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!

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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.

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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.

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5.9  Formulating Algorithms: Sentinel-Controlled Repetition (Cont..)

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5.10 Formulating Algorithms: Nested Control Statements

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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

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5.11 Compound Assignment Operators

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5.12 Increment and Decrement Operators

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// 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 }

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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.

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