Console Input / OutputConsole Input / OutputReading and Writing to the ConsoleReading and Writing to the Console

Svetlin NakovSvetlin NakovTelerik CorporationTelerik Corporationwww.telerik.comwww.telerik.com

Table of ContentsTable of Contents Printing to the ConsolePrinting to the Console

Printing Strings and Numbers Printing Strings and Numbers

Reading from the ConsoleReading from the Console

Reading CharactersReading Characters

Reading StringsReading Strings

Parsing Strings to Numeral TypesParsing Strings to Numeral Types

Reading Numeral TypesReading Numeral Types

Various ExamplesVarious Examples

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Printing to the ConsolePrinting to the ConsolePrinting Strings, Numeral Types and ExpressionsPrinting Strings, Numeral Types and Expressions

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Printing to the ConsolePrinting to the Console Console is used to display information in a text Console is used to display information in a text

windowwindow Can display different values:Can display different values:

StringsStrings

Numeral typesNumeral types

All primitiveAll primitive datadata typestypes

To print to the console use the class To print to the console use the class ConsoleConsole ((System.ConsoleSystem.Console))

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The Console ClassThe Console Class Provides methods for console input and outputProvides methods for console input and output

InputInput

Read(…)Read(…) – reads a single character – reads a single character

ReadKey(…)ReadKey(…) – reads a combination of keys– reads a combination of keys

ReadLine(…)ReadLine(…) – reads a single line of characters – reads a single line of characters

OutputOutput

Write(…)Write(…) – prints the specified – prints the specified argument on the consoleargument on the console

WriteLine(…WriteLine(…)) – prints specified data to the – prints specified data to the console and moves to the next lineconsole and moves to the next line

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Console.Write(…)Console.Write(…)

Printing more than one variable using a Printing more than one variable using a formatting stringformatting string

int a = 15;int a = 15;......Console.Write(a); // 15Console.Write(a); // 15

Printing an integer variablePrinting an integer variable

double a = 15.5;double a = 15.5;int b = 14;int b = 14;......Console.Write("{0} + {1} = {2}", a, b, a + b);Console.Write("{0} + {1} = {2}", a, b, a + b);// 15.5 + 14 = 29.5// 15.5 + 14 = 29.5

Next print operation will start from the same lineNext print operation will start from the same line6

Console.WriteLine(…)Console.WriteLine(…)

Printing more than one variable using a Printing more than one variable using a formatting stringformatting string

string str = "Hello C#!";string str = "Hello C#!";......Console.WriteLine(str);Console.WriteLine(str);

Printing a string variablePrinting a string variable

string name = "Marry";string name = "Marry";int year = 1987;int year = 1987;......Console.Write("{0} was born in {1}.", name, year);Console.Write("{0} was born in {1}.", name, year);// Marry was born in 1987.// Marry was born in 1987.

Next printing will start from the next lineNext printing will start from the next line7

Printing to the Console – ExamplePrinting to the Console – Example

static void Main()static void Main(){{ string name = "Peter";string name = "Peter"; int age = 18;int age = 18; string town = "Sofia";string town = "Sofia";

Console.Write("{0} is {1} years old from {2}.",Console.Write("{0} is {1} years old from {2}.", name, age, town);name, age, town); // Result: Peter is 18 years old from Sofia.// Result: Peter is 18 years old from Sofia. Console.Write("This is on the same line!");Console.Write("This is on the same line!"); Console.WriteLine("Next sentence will be" +Console.WriteLine("Next sentence will be" + " on a new line.");" on a new line.");

Console.WriteLine("Bye, bye, {0} from {1}.",Console.WriteLine("Bye, bye, {0} from {1}.", name, town);name, town);} }

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Using Parameters – ExampleUsing Parameters – Example

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static void Main()static void Main(){{ int a=2, b=3;int a=2, b=3; Console.Write("{0} + {1} =", a, b);Console.Write("{0} + {1} =", a, b); Console.WriteLine(" {0}", a+b);Console.WriteLine(" {0}", a+b); // 2 + 3 = 5// 2 + 3 = 5

Console.WriteLine("{0} * {1} = {2}",Console.WriteLine("{0} * {1} = {2}", a, b, a*b);a, b, a*b); // 2 * 3 = 6// 2 * 3 = 6

float pi = 3.14159206;float pi = 3.14159206; Console.WriteLine("{0:F2}", pi); // 3,14Console.WriteLine("{0:F2}", pi); // 3,14 Console.WriteLine("Bye – Bye!");Console.WriteLine("Bye – Bye!");} }

Printing a Menu – ExamplePrinting a Menu – Example

double colaPrice = 1.20;double colaPrice = 1.20;string cola = "Coca Cola";string cola = "Coca Cola";double fantaPrice = 1.20;double fantaPrice = 1.20;string fanta = "Fanta Dizzy";string fanta = "Fanta Dizzy";double zagorkaPrice = 1.50;double zagorkaPrice = 1.50;string zagorka = "Zagorka";string zagorka = "Zagorka";

Console.WriteLine("Menu:");Console.WriteLine("Menu:");Console.WriteLine("1. {0} – {1}",Console.WriteLine("1. {0} – {1}",

cola, colaPrice);cola, colaPrice);Console.WriteLine("2. {0} – {1}",Console.WriteLine("2. {0} – {1}",

fanta, fantaPrice);fanta, fantaPrice);Console.WriteLine("3. {0} – {1}",Console.WriteLine("3. {0} – {1}",

zagorka, zagorkaPrice);zagorka, zagorkaPrice);Console.WriteLine("Have a nice day!");Console.WriteLine("Have a nice day!");

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Printing to Printing to the Consolethe Console

Live DemoLive Demo

Reading from the ConsoleReading from the ConsoleReading Strings and Numeral TypesReading Strings and Numeral Types

Reading from the ConsoleReading from the Console We use the console to read information from We use the console to read information from

the command linethe command line We can read:We can read:

CharactersCharacters

StringsStrings

Numeral types (after conversion)Numeral types (after conversion)

To read from the console we use the methods To read from the console we use the methods Console.Read()Console.Read() and and Console.ReadLine()Console.ReadLine()

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Console.Read()Console.Read() Gets a single character from the console (after Gets a single character from the console (after

[Enter] is pressed)[Enter] is pressed)

Returns a result of type Returns a result of type intint

Returns Returns -1-1 if there aren’t more symbols if there aren’t more symbols

To get the actually read character we To get the actually read character we need to cast it to need to cast it to charchar

int i = Console.Read();int i = Console.Read();char ch = (char) i; // Cast the int to charchar ch = (char) i; // Cast the int to char

// Gets the code of the entered symbol// Gets the code of the entered symbolConsole.WriteLine("The code of '{0}' is {1}.", ch, i);Console.WriteLine("The code of '{0}' is {1}.", ch, i);

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Reading Characters Reading Characters fromfrom the Consolethe Console

Live DemoLive Demo

Console.ReadKey()Console.ReadKey() Waits until a combination of keys is pressedWaits until a combination of keys is pressed

Reads a single character from console or a Reads a single character from console or a combination of keyscombination of keys

Returns a result of type Returns a result of type ConsoleKeyInfoConsoleKeyInfo

KeyCharKeyChar – holds the entered character – holds the entered character

ModifiersModifiers – holds the state of [Ctrl], [Alt], … – holds the state of [Ctrl], [Alt], …

ConsoleKeyInfo key = Console.ReadKey();ConsoleKeyInfo key = Console.ReadKey();Console.WriteLine();Console.WriteLine();Console.WriteLine("Character entered: " + key.KeyChar);Console.WriteLine("Character entered: " + key.KeyChar);Console.WriteLine("Special keys: " + key.Modifiers);Console.WriteLine("Special keys: " + key.Modifiers);

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Reading Keys Reading Keys from the Consolefrom the Console

Live DemoLive Demo

Console.ReadLine()Console.ReadLine()

Gets a line of charactersGets a line of characters

Returns a Returns a stringstring value value

Returns Returns nullnull if the end of the input is reached if the end of the input is reached

Console.Write("Please enter your first name: ");Console.Write("Please enter your first name: ");string firstName = Console.ReadLine();string firstName = Console.ReadLine();

Console.Write("Please enter your last name: ");Console.Write("Please enter your last name: ");string lastName = Console.ReadLine();string lastName = Console.ReadLine();

Console.WriteLine("Hello, {0} {1}!",Console.WriteLine("Hello, {0} {1}!", firstName, lastName);firstName, lastName);

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Reading Strings Reading Strings from the Consolefrom the Console

Live DemoLive Demo

Reading Numeral TypesReading Numeral Types Numeral types can not be read directly from the Numeral types can not be read directly from the

consoleconsole

To read a numeral type do the following:To read a numeral type do the following:

l RRead a string valueead a string value

u Convert (parse) it to the required numeral typeConvert (parse) it to the required numeral type

int.Parse(string)int.Parse(string) – parses a – parses a stringstring to to intint

string str = Console.ReadLine()string str = Console.ReadLine()int number = int.Parse(str);int number = int.Parse(str);

Console.WriteLine("You entered: {0}", number);Console.WriteLine("You entered: {0}", number);

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Converting Strings to NumbersConverting Strings to Numbers Numeral types have a method Numeral types have a method Parse(…)Parse(…) for for

extracting the numeral value from a stringextracting the numeral value from a string

int.Parse(string)int.Parse(string) – – stringstring intint

longlong.Parse(string).Parse(string) – – stringstring longlong

floatfloat.Parse(string).Parse(string) – – stringstring floatfloat

Causes Causes FormatExceptionFormatException in case ofin case of errorerrorstring s = "123";string s = "123";int i = int.Parse(s); // i = 123int i = int.Parse(s); // i = 123long l = long.Parse(s); // l = 123Llong l = long.Parse(s); // l = 123L

string invalid = "xxx1845";string invalid = "xxx1845";int value = int.Parse(invalid); // FormatExceptionint value = int.Parse(invalid); // FormatException

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Reading Numbers from the Reading Numbers from the Console – ExampleConsole – Example

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static void Main()static void Main(){{ int a = int.Parse(Console.ReadLine());int a = int.Parse(Console.ReadLine()); int b = int.Parse(Console.ReadLine());int b = int.Parse(Console.ReadLine());

Console.WriteLine("{0} + {1} = {2}",Console.WriteLine("{0} + {1} = {2}", a, b, a+b);a, b, a+b); Console.WriteLine("{0} * {1} = {2}",Console.WriteLine("{0} * {1} = {2}", a, b, a*b);a, b, a*b);

float f = float.Parse(Console.ReadLine());float f = float.Parse(Console.ReadLine()); Console.WriteLine("{0} * {1} / {2} = {3}",Console.WriteLine("{0} * {1} / {2} = {3}", a, b, f, a*b/f);a, b, f, a*b/f);}}

Converting Strings to Converting Strings to Numbers (2)Numbers (2)

Converting can also be done using the methods of Converting can also be done using the methods of the the ConvertConvert class class

Convert.ToInt32(string)Convert.ToInt32(string) – – stringstring intint

Convert.ToSingle(string)Convert.ToSingle(string)– – stringstring floatfloat

Convert.ToInt64(string)Convert.ToInt64(string)– – stringstring longlong

Internally uses the parse methods of the numeral Internally uses the parse methods of the numeral typestypes

string s = "123";string s = "123";int i = Convert.ToInt32(s); // i = 123int i = Convert.ToInt32(s); // i = 123long l = Convert.ToInt64(s); // l = 123Llong l = Convert.ToInt64(s); // l = 123L

string invalid = "xxx1845";string invalid = "xxx1845";int value = Convert.ToInt32(invalid); // FormatExceptionint value = Convert.ToInt32(invalid); // FormatException

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Reading Numbers Reading Numbers from the Consolefrom the Console

Live DemoLive Demo

Error Handling when ParsingError Handling when Parsing Sometimes we want to handle the errors when Sometimes we want to handle the errors when

parsing a numberparsing a number

Two options: use Two options: use trytry--catchcatch block or block or TryParse()TryParse()

Parsing with Parsing with TryParse()TryParse()::string str = Console.ReadLine();string str = Console.ReadLine();int number;int number;if (int.TryParse(str, out number))if (int.TryParse(str, out number)){{ Console.WriteLine("Valid number: {0}", number);Console.WriteLine("Valid number: {0}", number);}}elseelse{{ Console.WriteLine("Invalid number: {0}", str);Console.WriteLine("Invalid number: {0}", str);}}

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Parsing with Parsing with TryParseTryParse()()Live DemoLive Demo

Reading and Printing Reading and Printing to the Consoleto the Console

Various ExamplesVarious Examples

Printing a Letter – ExamplePrinting a Letter – Example

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Console.Write("Enter person name: ");Console.Write("Enter person name: ");string person = Console.ReadLine();string person = Console.ReadLine();

Console.Write("Enter company name: ");Console.Write("Enter company name: ");string company = Console.ReadLine();string company = Console.ReadLine();

Console.WriteLine(" Dear {0},", person);Console.WriteLine(" Dear {0},", person);Console.WriteLine("We are pleased to tell you " + Console.WriteLine("We are pleased to tell you " + "that {1} has chosen you to take part " +"that {1} has chosen you to take part " + "in the \"Introduction To Programming\" " + "in the \"Introduction To Programming\" " + "course. {1} wishes you good luck!","course. {1} wishes you good luck!", person, company);person, company);

Console.WriteLine(" Yours,");Console.WriteLine(" Yours,");Console.WriteLine(" {0}", company);Console.WriteLine(" {0}", company);

Printing a LetterPrinting a LetterLive DemoLive Demo

Calculating Area – ExampleCalculating Area – Example

Console.WriteLine("This program calculates " +Console.WriteLine("This program calculates " + "the area of a rectangle or a triangle");"the area of a rectangle or a triangle");

Console.Write("Enter a and b (for rectangle) " +Console.Write("Enter a and b (for rectangle) " + " or a and h (for triangle): ");" or a and h (for triangle): ");int a = int.Parse(Console.ReadLine());int a = int.Parse(Console.ReadLine());int b = int.Parse(Console.ReadLine());int b = int.Parse(Console.ReadLine());

Console.Write("Enter 1 for a rectangle or 2 " +Console.Write("Enter 1 for a rectangle or 2 " + "for a triangle: ");"for a triangle: ");

int choice = int.Parse(Console.ReadLine());int choice = int.Parse(Console.ReadLine());double area = (double) (a*b) / choice;double area = (double) (a*b) / choice;Console.WriteLine("The area of your figure " +Console.WriteLine("The area of your figure " + " is {0}", area);" is {0}", area);

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Calculating AreaCalculating AreaLive DemoLive Demo

SummarySummary We have discussed the basic input and output We have discussed the basic input and output

methods of the classmethods of the class ConsoleConsole

Write(…)Write(…) and and WriteLine(WriteLine(……))

Used to write values to the consoleUsed to write values to the console

Read(…)Read(…) and and ReadLine(ReadLine(……))

Used to read values from the consoleUsed to read values from the console

Parsing numbers to stringsParsing numbers to strings

int.Parse(…)int.Parse(…), , double.Parse(…)double.Parse(…), …, …

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Questions?Questions?

Console Input / OutputConsole Input / Output

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ExercisesExercises

1.1. Write a program that reads Write a program that reads 33 integer numbers from integer numbers from the console and prints their sum.the console and prints their sum.

2.2. Write a program that reads the radius Write a program that reads the radius rr of a circle of a circle and prints its perimeter and area.and prints its perimeter and area.

3.3. A company has name, address, phone number, fax A company has name, address, phone number, fax number, web site and manager. The manager has number, web site and manager. The manager has first name, last name, age and a phone number. first name, last name, age and a phone number. Write a program that reads the information about a Write a program that reads the information about a company and its manager and prints them on the company and its manager and prints them on the console.console.

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Exercises (2)Exercises (2)

1.1. Write a program that reads two positive integer Write a program that reads two positive integer numbers and prints how many numbers numbers and prints how many numbers pp exist exist between them such that the reminder of the division between them such that the reminder of the division by by 55 is is 00 (inclusive). Example: (inclusive). Example: p(17,25)p(17,25) == 22..

2.2. Write a program that gets two numbers from the Write a program that gets two numbers from the console and prints the greater of them. Don’t use console and prints the greater of them. Don’t use ifif statements.statements.

3.3. Write a program that reads the coefficients Write a program that reads the coefficients aa, , bb and and cc of a quadratic equation of a quadratic equation aaxx22+b+bxx+c=0+c=0 and solves it and solves it (prints its real roots).(prints its real roots).

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Exercises (3)Exercises (3)

1.1. Write a program that gets a number Write a program that gets a number nn and after that and after that gets more gets more nn numbers and calculates and prints their numbers and calculates and prints their sum. sum.

2.2. Write a program that reads an integer number Write a program that reads an integer number nn from the console and prints all the numbers in the from the console and prints all the numbers in the interval [interval [11....nn], each on a single line.], each on a single line.

3.3. Write a program to print the first 100 members of Write a program to print the first 100 members of the sequence of Fibonaccithe sequence of Fibonacci: 0, 1, 1, 2, 3, 5, 8, 13, 21, : 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, …34, 55, 89, 144, 233, 377, …

4.4. Write a program to calculate the sum (with accuracy Write a program to calculate the sum (with accuracy of 0.001): 1 + 1/2 - 1/3 + 1/4 - 1/5 + ...of 0.001): 1 + 1/2 - 1/3 + 1/4 - 1/5 + ...

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