04. Console Input Output

Console Input / Output
Reading and Writing to the Console
Svetlin Nakov
Technical Trainer
www.nakov.com
Software University
http://softuni.bg

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1. Printing to the Console
 Printing Strings and Numbers
2. Reading from the Console
 Reading Characters
 Reading Strings
 Parsing Strings to Numeral Types
 Reading Numeral Types
3. Various Examples
Table of Contents

Printing to the Console
Printing Strings, Numeral Types
and Expressions

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 The console (terminal window) is used to read / display text-
based information in a virtual terminal window
 Learn more from Wikipedia: terminal emulator, virtual console
 Can display different values:
 Strings
 Numeral types
 All primitive data types
 To print to the console use the
Console class (System.Console)
Printing to the Console

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 Provides methods for console input and output
 Input
 Read(…) – reads a single character
 ReadKey(…) – reads a combination of keys
 ReadLine(…) – reads a single line of characters
 Output
 Write(…) – prints the specified argument on the console
 WriteLine(…) – prints specified data to the console and moves
to the next line
The Console Class

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 Printing an integer variable:
 Printing more than one variable using a formatting string:
Console.Write(…)
int a = 15;
Console.Write(a); // 15
double a = 15.5;
int b = 14;
...
Console.Write("{0} + {1} = {2}", a, b, a + b);
// 15.5 + 14 = 29.5
 The next print operation will start from the same line

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Console.WriteLine(…)
 Printing more than one variable using a formatting string:
string str = "Hello C#!";
Console.WriteLine(str);
 Printing a string variable + new line (rn):
string name = "Marry";
int year = 1987;
...
Console.WriteLine("{0} was born in {1}.", name, year);
// Marry was born in 1987.
 Next printing will start from the new line

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Printing to the Console – Example
static void Main()
{
string name = "Peter";
int age = 18;
string town = "Sofia";
Console.Write("{0} is {1} years old from {2}.",
name, age, town);
// Result: Peter is 18 years old from Sofia.
Console.Write("This is on the same line!");
Console.WriteLine("Next sentence will be on a new line.");
Console.WriteLine("Bye, bye, {0} from {1}.", name, town);
}

 index
 The zero-based index of the argument whose string
representation is to be included at this position in the string
 alignment
 A signed integer that indicates the total length of the field into
which the argument is inserted
 a positive integer – right-aligned
 a negative integer – left-aligned
Formatting Strings
{index[,alignment][:formatString]}

 formatString
 Specifies the format of the corresponding argument's result string,
e.g. "X", "C", "0.00", e.g.
Formatting Strings (2)
static void Main()
{
double pi = 1.234;
Console.WriteLine("{0:0.000000}", pi);
// 1.234000
}
{index[,alignment][:formatString]}

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Formatting Strings – Examples
static void Main()
{
int a=2, b=3;
Console.Write("{0} + {1} =", a, b);
Console.WriteLine(" {0}", a+b);
// 2 + 3 = 5
Console.WriteLine("{0} * {1} = {2}", a, b, a*b);
// 2 * 3 = 6
float pi = 3.14159206;
Console.WriteLine("{0:F2}", pi); // 3,14 or 3.14
Console.WriteLine("Bye – Bye!");
}

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Printing a Menu – Example
double colaPrice = 1.20;
string cola = "Coca Cola";
double fantaPrice = 1.20;
string fanta = "Fanta Dizzy";
double zagorkaPrice = 1.50;
string zagorka = "Zagorka";
Console.WriteLine("Menu:");
Console.WriteLine("1. {0} – {1}", cola, colaPrice);
Console.WriteLine("2. {0} – {1}", fanta, fantaPrice);
Console.WriteLine("3. {0} – {1}", zagorka, zagorkaPrice);
Console.WriteLine("Have a nice day!");

Printing to
the Console
Live Demo

Reading from the Console
Reading Strings and Numeral Types

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 We use the console to read information from the command line
 Usually the data is entered from the keyboard
 We can read:
 Characters
 Strings
 Numeral types (after conversion)
 To read from the console we use the methods
Console.Read() and Console.ReadLine()
Reading from the Console

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 Gets a single character from the console (after [Enter] is
pressed)
 Returns a result of type int
 Returns -1 if there aren’t more symbols
 To get the actually read character we need to cast it to char
Console.Read()
int i = Console.Read();
char ch = (char) i; // Cast the int to char
// Gets the code of the entered symbol
Console.WriteLine("The code of '{0}' is {1}.", ch, i);

Reading Characters
from the Console
Live Demo

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 Waits until a combination of keys is pressed
 Reads a single character from console or a combination of keys
 Returns a result of type ConsoleKeyInfo
 KeyChar – holds the entered character
 Modifiers – holds the state of [Ctrl], [Alt], …
Console.ReadKey()
ConsoleKeyInfo key = Console.ReadKey();
Console.WriteLine();
Console.WriteLine("Character entered: " + key.KeyChar);
Console.WriteLine("Special keys: " + key.Modifiers);

Reading Keys from the Console
Live Demo

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 Gets a line of characters
 Returns a string value
 Returns null if the end of the input is reached
Console.ReadLine()
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, {0} {1}!", firstName, lastName);

Reading Strings from the Console
Live Demo

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 Numeral types can not be read directly from the console
 To read a numeral type do the following:
1. Read a string value
2. Convert (parse) it to the required numeral type
 int.Parse(string)
 Parses (converts) a string to int
Reading Numeral Types
string str = Console.ReadLine()
int number = int.Parse(str);
Console.WriteLine("You entered: {0}", number);

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 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
Converting Strings to Numbers
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
static void Main()
{
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
Console.WriteLine("{0} + {1} = {2}", a, b, a+b);
Console.WriteLine("{0} * {1} = {2}", a, b, a*b);
float f = float.Parse(Console.ReadLine());
Console.WriteLine("{0} * {1} / {2} = {3}", a, b, f, a*b/f);
}

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 Converting can also be done through the Convert class
 Convert.ToInt32(string[, base]) – string  int
 Convert.ToSingle(string)– string  float
 Convert.ToInt64(string)– string  long
 It uses the parse methods of the numeral types
Converting Strings to Numbers (2)
string s = "123";
int i = Convert.ToInt32(s); // i = 123
long l = Convert.ToInt64(s); // l = 123L
string invalid = "xxx1845";
int value = Convert.ToInt32(invalid); // FormatException

Reading Numbers from the Console
Live Demo

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 Sometimes we want to handle the errors when parsing a number
 Two options: use try-catch block or TryParse()
 Parsing with TryParse():
Error Handling when Parsing
string str = Console.ReadLine();
int number;
if (int.TryParse(str, out number))
{
Console.WriteLine("Valid number: {0}", number);
}
else
{
Console.WriteLine("Invalid number: {0}", str);
}

Parsing with TryParse()
Live Demo

Regional Settings
Printing and Reading Special Characters
Regional Settings and the Number Formatting

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 Printing special characters on the console needs two steps:
 Change the console properties
to enable Unicode-friendly font
 Enable Unicode for the Console
by adjusting its output encoding
 Prefer UTF8 (Unicode)
How to Print Special Characters on the Console?
using System.Text;
…
Console.OutputEncoding = Encoding.UTF8;
Console.WriteLine("Това е кирилица: ☺");

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 The currency format and number formats are different in
different countries
 E.g. the decimal separator could be "." or ","
 To ensure the decimal separator is "." use the following code:
Decimal Separator
using System.Threading;
using System.Globalization;
…
Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;
Console.WriteLine(3.54); // 3.54
decimal value = decimal.Parse("1.33");

Reading and Printing to the Console
Various Examples

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Printing a Letter – Example
Console.Write("Enter person name: ");
string person = Console.ReadLine();
Console.Write("Enter company name: ");
string company = Console.ReadLine();
Console.WriteLine(" Dear {0},", person);
Console.WriteLine("We are pleased to tell you that " +
"{1} has accepted you to take part in the "C# Basics"" +
" course. {1} wishes you a good luck!", person, company);
Console.WriteLine(" Yours,");
Console.WriteLine(" {0}", company);

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Calculating Area – Example
Console.WriteLine("This program calculates " +
"the area of a rectangle or a triangle");
Console.Write("Enter a and b (for rectangle) " +
" or a and h (for triangle): ");
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
Console.Write("Enter 1 for a rectangle or 2 for a triangle: ");
int choice = int.Parse(Console.ReadLine());
double area = (double) (a*b) / choice;
Console.WriteLine("The area of your figure is {0}", area);

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 Basic input and output methods of the class Console
 Write(…) and WriteLine(…)
 Write values to the console
 Read(…) and ReadLine(…)
 Read values from the console
 Parsing numbers to strings
 int.Parse(…)
 double.Parse(…)
 …
Summary

?
http://softuni.bg/courses/csharp-basics/
Console Input / Output

License
 This course (slides, examples, demos, videos, homework, etc.)
is licensed under the "Creative Commons Attribution-
NonCommercial-ShareAlike 4.0 International" license
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 Attribution: this work may contain portions from
 "Fundamentals of Computer Programming with C#" book by Svetlin Nakov & Co. under CC-BY-SA license
 "C# Part I" course by Telerik Academy under CC-BY-NC-SA license

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04. Console Input Output

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