theme: Next, 1

[fit] Interacting with the console

Interacting with the console

• Computers, and thus software, are good at accepting input, processing it, and producing new information.
• The applications we write in this program will certainly fit that pattern.
• With our first programs we'd like to interact with the user directly in our shell.

^ In other lessons we will learn to interact with the user via an API and via a web page.

[.column]

Example

[.column]

^ We'd like our programs to be able to input information and then be able to output information. Like asking for a name and then greeting the user.

[fit] Sending information to the console

• Interactions with the console use the Console class. In a different lesson we will cover classes. _{For now know that a class can be a collection of code.}
• We will use a few different statements:
  • Console.WriteLine()
  • Console.Write()
  • Console.ReadLine()

[fit] Outputting to the console one line at a time

Console.WriteLine("Welcome to my program");

This will output one line to the console and move the cursor to the next line. Further output will be on its own line.

[fit] Outputting a blank line

Console.WriteLine("");

[fit] Output text but do not move the cursor to the next line

[.column]

To leave the cursor on the same line as the text use Console.Write().

In this case the cursor remains in place after the last character of our output. In this case we leave a blank space.

[.column]

Console.Write("What is your name? ");

[fit] Reading information from the console

[.column]

To read information we use Console.ReadLine()

This pauses our program for the user to type in text and press ENTER.

Then assigns the answer to a string variable we place on the left-hand-side.

[.column]

var name = Console.ReadLine();

[fit] Outputting information containing a variable

First print out the fixed text

But don't move the cursor to the next line yet

[.code-highlight: 1]

Console.Write("It is a pleasure to meet you,");
Console.WriteLine(name);

Then print out the variable

And move the cursor to the next line

[.code-highlight: 2]

Console.Write("It is a pleasure to meet you,");
Console.WriteLine(name);

[fit] We can do better

[fit] Strings can be added together!

var greeting = "It is a pleasure to meet you, " + name;
Console.WriteLine(greeting);

[fit] Avoid writing the variable

Since we create the greeting variable just to use it once we can get rid of it.

Console.WriteLine("It is a pleasure to meet you, " + name);

[fit] Avoid the + string addition

This pattern of using a variable along with a string is so common C# gives us a way to do this right inside the string!

String interpolation

If we put a $ before our first double quote the string gains magic powers.

[fit] String interpolation

$"It is a pleasure to meet you, {name}"

Inside a string with the $ powers we can place {} inside the string. Anything inside the string is considered code.

Whatever that code evaluates to is placed at that spot in the string!

$"My favorite number is {6 * 7}";

[fit] Using string interpolation

Console.WriteLine($"It is a pleasure to meet you, {name}");

Full program

using System;
namespace OurDotNetApp
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Welcome to my program");
      Console.WriteLine("\n");
      Console.Write("What is your name? ");
      var name = Console.ReadLine();
      Console.WriteLine($"It is a pleasure to meet you, {name}");
    }
  }
}