Console

Console programs communicate through text. Many features are available in C#: Console.WriteLine renders a line of text. Console.ReadLine gets user input.

For console output, we can use format strings and colors. A red warning message can be written. These features are helpful when developing with the "dotnet" command line program.

WriteLine

There are many overloads on Console.WriteLine. An overloaded method has the same name but accepts different parameters.

using System;

// Part 1: write an int with Console.WriteLine.
int valueInt = 4;
Console.WriteLine(valueInt);

// Part 2: write a string with the method.
string valueString = "Your string";
Console.WriteLine(valueString);

// Part 3: write a bool with the method.
bool valueBool = false;
Console.WriteLine(valueBool);
4
Your string
False

Empty line

It is possible to use Console.WriteLine with no arguments. This will simply output a blank line to the Console window. This is an elegant way to output an empty line.

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("A");
        Console.WriteLine(); // Empty line.
        Console.WriteLine("B");
    }
}
A

B

Console, Concat

In some programs, we will want to write several values on a single line to the Console. We can form a string using the "+" operator before passing it to Console.WriteLine.

using System;

class Program
{
    static void Main()
    {
        string name = "USER";
        int id = 100;
        // A string is created before WriteLine is called.
        Console.WriteLine(name + ": " + id);
    }
}
USER: 100

Console, Write

We can combine the Console.Write method with the Console.WriteLine method. Both methods can be used on the same line. Write() does not append a newline to the end.

using System;

class Program
{
    static void Main()
    {
        string name = "USER";
        int id = 100;
        // Write 3 parts to the same line.
        Console.Write(name);
        Console.Write(": ");
        Console.WriteLine(id);
    }
}
USER: 100

String, formats

A format string is often clearest. Here the first parameter is a literal that has N substitution places. The next N parameters are inserted in those places.

using System;

class Program
{
    static void Main()
    {
        string value1 = "Dot";
        string value2 = "Net";
        string value3 = "Perls";

        Console.WriteLine("{0}, {1}, {2}",
            value1,
            value2,
            value3);
    }
}
Dot, Net, Perls

Char arrays

This is an advanced feature of Console.WriteLine. It writes an entire char array to the screen. Char arrays are useful in optimization code and sometimes interop or DLL code.

using System;

class Program
{
    static void Main()
    {
        char[] array = new char[] { 'a', 'b', 'c', 'd' };
        // ... Write the entire char array on a line.
        Console.WriteLine(array);
        // ... Write the middle 2 characters on a line.
        Console.WriteLine(array, 1, 2);
    }
}
abcd
bc

ToString

When we pass an object to the Console.WriteLine method, it invokes the ToString override method on the class (if one exists). Here we see this happen with a Test class.

using System;

class Test
{
    public override string ToString()
    {
        // Printed by Console.WriteLine.
        return "Test object string";
    }
}

class Program
{
    static void Main()
    {
        // Create class with ToString method.
        Test test = new Test();
        // WriteLine calls to the ToString method.
        Console.WriteLine(test);
    }
}
Test object string

Using static System.Console

Suppose we want to avoid typing "Console" in our program to save time. We can add "using static System.Console" to the top.

using static System.Console;

class Program
{
    static void Main()
    {
        // We can just write WriteLine instead of Console.WriteLine.
        // ... This saves exactly 8 characters.
        WriteLine("Hello my friend!");
    }
}
Hello my friend!

Title

Here we use a loop and set the Console.Title property to whatever the user typed into the console. We can change the title of the console window by entering text.

using System;

class Program
{
    static void Main()
    {
        while (true)
        {
            // Assign Console.Title property to string returned by ReadLine.
            Console.Title = Console.ReadLine();
        }
    }
}

CapsLock

This program prints the value returned by Console.CapsLock every 1 second. Try pressing the caps lock key. It will start printing True when the key is pressed.

using System;
using System.Threading;

class Program
{
    static void Main()
    {
        while (true)
        {
            Thread.Sleep(1000);
            bool capsLock = Console.CapsLock;
            Console.WriteLine(capsLock);
        }
    }
}
False
False
True
True
True
False
True
True

NumberLock

This program prints to the console every 1 second. As it executes, we can press Num Lock and the output of the program will change.

using System;
using System.Threading;

class Program
{
    static void Main()
    {
        while (true)
        {
            Console.WriteLine(Console.NumberLock);
            Thread.Sleep(1000);
        }
    }
}
False
False
True
True
False
False

Height, width

With WindowWidth, we control the width of a window based on the number of text columns. Height changes the window size based on lines of text.

using System;

class Program
{
    static void Main()
    {
        // ... Width is the number of columns of text.
        Console.WindowWidth = 40;
        // ... Height is the number of lines of text.
        Console.WindowHeight = 10;
        // ... Say hello.
        Console.WriteLine("Hi");
    }
}

Benchmark, console

In many simple console programs, the Console.WriteLine may be one of the biggest slowdowns. Here we time 100 lines written to the console.

using System;
using System.Diagnostics;
using System.Text;

class Program
{
    static void Main()
    {
        int version = 1;
        var t1 = Stopwatch.StartNew();
        if (version == 1)
        {
            // Version 1: write 100 separate lines.
            for (int i = 0; i < 100; i++)
            {
                Console.WriteLine("x");
            }
        }
        else if (version == 2)
        {
            // Version 2: write 100 lines as a single string.
            StringBuilder temp = new StringBuilder();
            for (int i = 0; i < 100; i++)
            {
                temp.AppendLine("x");
            }
            Console.WriteLine(temp.ToString());
        }

        // Results.
        Console.WriteLine("TIME FOR VERSION {0}: {1} ms", version, t1.ElapsedMilliseconds);
    }
}
TIME FOR VERSION 1: 35 ms
TIME FOR VERSION 2: 3 ms

Review

Console.WriteLine is a useful method. At first, it may seem less interesting than others. But then we realize how many programs in C# can be written with just console output.