Console Input / Output Reading and Writing to the Console

Содержание

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Table of Contents Printing to the Console Printing Strings and Numbers

Table of Contents

Printing to the Console
Printing Strings and Numbers
Reading from

the Console
Reading Characters
Reading Strings
Parsing Strings to Numeral Types
Reading Numeral Types
Various Examples
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Printing to the Console Printing Strings, Numeral Types and Expressions

Printing to the Console

Printing Strings, Numeral Types and Expressions

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Printing to the Console Console is used to display information in

Printing to the Console

Console is used to display information in a

text window
Can display different values:
Strings
Numeral types
All primitive data types
To print to the console use the class Console (System.Console)
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The Console Class Provides methods for console input and output Input

The Console Class

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
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Console.Write(…) Printing more than one variable using a formatting string int

Console.Write(…)

Printing more than one variable using a formatting string

int a =

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

Printing an integer variable

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

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

Console.WriteLine(…)

Printing more than one variable using a formatting string

string str =

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

Printing a string variable

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

Next printing will start from the next line

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Printing to the Console – Example static void Main() { string

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);
}
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Using Parameters – Example static void Main() { int a=2, b=3;

Using Parameters – Example

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
Console.WriteLine("Bye – Bye!");
}
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Printing a Menu – Example double colaPrice = 1.20; string cola

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!");
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Printing to the Console Live Demo

Printing to the Console

Live Demo

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Reading from the Console Reading Strings and Numeral Types

Reading from the Console

Reading Strings and Numeral Types

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Reading from the Console We use the console to read information

Reading from the Console

We use the console to read information from

the command line
We can read:
Characters
Strings
Numeral types (after conversion)
To read from the console we use the methods Console.Read() and Console.ReadLine()
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Console.Read() Gets a single character from the console (after [Enter] is

Console.Read()

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

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);

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Reading Characters from the Console Live Demo

Reading Characters from the Console

Live Demo

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

Console.ReadKey()

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], …

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

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Reading Keys from the Console Live Demo

Reading Keys from the Console

Live Demo

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Console.ReadLine() Gets a line of characters Returns a string value Returns

Console.ReadLine()

Gets a line of characters
Returns a string value
Returns null if the

end of the input is reached

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);

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Reading Strings from the Console Live Demo

Reading Strings from the Console

Live Demo

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Reading Numeral Types Numeral types can not be read directly from

Reading Numeral Types

Numeral types can not be read directly from the

console
To read a numeral type do the following:
Read a string value
Convert (parse) it to the required numeral type
int.Parse(string) – parses a string to int

string str = Console.ReadLine()
int number = int.Parse(str);
Console.WriteLine("You entered: {0}", number);

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

Converting Strings to Numbers

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

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() {

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 Strings to Numbers (2) Converting can also be done using

Converting Strings to Numbers (2)

Converting can also be done using the

methods of the Convert class
Convert.ToInt32(string) – string ? int
Convert.ToSingle(string)– string ? float
Convert.ToInt64(string)– string ? long
Internally uses the parse methods of the numeral types

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

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Reading Numbers from the Console Live Demo

Reading Numbers from the Console

Live Demo

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Error Handling when Parsing Sometimes we want to handle the errors

Error Handling when Parsing

Sometimes we want to handle the errors when

parsing a number
Two options: use try-catch block or TryParse()
Parsing with TryParse():

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);
}

Слайд 26

Parsing with TryParse() Live Demo

Parsing with TryParse()

Live Demo

Слайд 27

Reading and Printing to the Console Various Examples Examples

Reading and Printing to the Console

Various Examples

Examples

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Printing a Letter – Example Console.Write("Enter person name: "); string person

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 chosen you to take part " +
"in the \"Introduction To Programming\" " +
"course. {1} wishes you good luck!",
person, company);
Console.WriteLine(" Yours,");
Console.WriteLine(" {0}", company);
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Printing a Letter Live Demo

Printing a Letter

Live Demo

Слайд 30

Calculating Area – Example Console.WriteLine("This program calculates " + "the area

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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Calculating Area Live Demo

Calculating Area

Live Demo

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Summary We have discussed the basic input and output methods of

Summary

We have discussed the basic input and output methods of the

class Console
Write(…) and WriteLine(…)
Used to write values to the console
Read(…) and ReadLine(…)
Used to read values from the console
Parsing numbers to strings
int.Parse(…), double.Parse(…), …
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Exercises Write a program that reads 3 integer numbers from the

Exercises

Write a program that reads 3 integer numbers from the console

and prints their sum.
Write a program that reads the radius r of a circle and prints its perimeter and area.
A company has name, address, phone number, fax number, web site and manager. The manager has first name, last name, age and a phone number. Write a program that reads the information about a company and its manager and prints them on the console.
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Exercises (2) Write a program that reads two positive integer numbers

Exercises (2)

Write a program that reads two positive integer numbers and

prints how many numbers p exist between them such that the reminder of the division by 5 is 0 (inclusive). Example: p(17,25) = 2.
Write a program that gets two numbers from the console and prints the greater of them. Don’t use if statements.
Write a program that reads the coefficients a, b and c of a quadratic equation ax2+bx+c=0 and solves it (prints its real roots).
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