C# Examples

Strings

// This program demonstrates string functions.

using System;

class Strings 
{
    public static void Main (string[] args) 
    {
        String str = "Hello";

        Console.WriteLine("string: " + str);
        Console.WriteLine("string.ToLower(): " + str.ToLower());
        Console.WriteLine("string.ToUpper(): " + str.ToUpper());
        Console.WriteLine("string.IndexOf('e'): " + str.IndexOf('e'));
        Console.WriteLine("string.Length: " + str.Length);
        Console.WriteLine("string.Replace('H', 'j'): " + str.Replace('H', 'j'));
        Console.WriteLine("string(Substring(2, 2)): " + str.Substring(2, 2));
        Console.WriteLine("string.Trim(): " + str.Trim());

        String name = "Bob";
        double value = 123.456;
        Console.WriteLine(String.Format("{0} earned {1:$0.00}", name, value));
    }
}

Output

string: Hello
string.ToLower(): hello
string.ToUpper(): HELLO
string.IndexOf('e'): 1
string.Length: 5
string.Replace('H', 'j'): jello
string(Substring(2, 2)): ll
string.Trim(): Hello
Bob earned $123.46

Files

// This program creates a file, adds data to the file, displays the file,
// appends more data to the file, displays the file, and then deletes the file.
// It will not run if the file already exists.
//
// References:
//     https://www.mathsisfun.com/temperature-conversion.html
//     https://en.wikibooks.org/wiki/C_Sharp_Programming

using System;

public class Files
{
    public static void Main(String[] args)
    {
        string FILENAME = "~file.txt";
    
        if(System.IO.File.Exists(FILENAME))
        {
            System.Console.WriteLine("File already exists.\n");
        }
        else
        {
            CreateFile(FILENAME);
            ReadFile(FILENAME);
            AppendFile(FILENAME);
            ReadFile(FILENAME);
            DeleteFile(FILENAME);
        }
    }
    
    private static double CalculateFahrenheit(double celsius)
    {
        double fahrenheit;

        fahrenheit = celsius * 9 / 5 + 32;
        return fahrenheit;
    }

    private static void CreateFile(string filename)
    {
        System.IO.StreamWriter file;
        double celsius;
        double fahrenheit;
        
        try
        {
            using(file = System.IO.File.CreateText(filename)) 
            {
                file.WriteLine("Celsius,Fahrenheit");
                for(celsius = 0; celsius <= 50; celsius++)
                {
                    fahrenheit = CalculateFahrenheit(celsius);
                    file.WriteLine(String.Format("{0:F1},{1:F1}", celsius, fahrenheit));
                }
            }
        }
        catch(Exception exception)
        {
            Console.WriteLine("Error creating " + filename);
            Console.WriteLine(exception.Message);
        }
    }
    
    private static void ReadFile(string filename)
    {
        System.IO.StreamReader file;
        string line;

        try
        {
            using (file = System.IO.File.OpenText(filename))
            {
                while (true) 
                {
                    line = file.ReadLine();
                    if (line == null)
                    {
                        break;
                    }
                    Console.WriteLine(line);
                }
            }
            Console.WriteLine("");
        }
        catch(Exception exception)
        {
            Console.WriteLine("Error reading " + filename);
            Console.WriteLine(exception.Message);
        }
    }
    
    private static void AppendFile(string filename)
    {
        System.IO.StreamWriter file;
        double celsius;
        double fahrenheit;
        
        try
        {
            using (file = System.IO.File.AppendText(filename))
            {
                for(celsius = 51; celsius <= 100; celsius++)
                {
                    fahrenheit = CalculateFahrenheit(celsius);
                    file.WriteLine(String.Format("{0:F1},{1:F1}", celsius, fahrenheit));
                }
            }
        }
        catch(Exception exception)
        {
            Console.WriteLine("Error appending to " + filename);
            Console.WriteLine(exception.Message);
        }
    }
    
    private static void DeleteFile(string filename)
    {
        try
        {
            System.IO.File.Delete(filename);
        }
        catch(Exception exception)
        {
            Console.WriteLine("Error deleting " + filename);
            Console.WriteLine(exception.Message);
        }
    }
}

Output

Celsius,Fahrenheit
0.0,32.0
1.0,33.8
2.0,35.6
...
98.0,208.4
99.0,210.2
100.0,212.0

References

• Wikiversity: Computer Programming