Summary  
Demonstrates file I/O by reading numeric data from two files, parsing and iterating through corresponding values to apply a user-selected arithmetic operation, then writing the results to a new file.

General domain of usage  
Batch file data processing

You can download the required folder for this task. The folder includes two files called `1.txt` and `2.txt`. 

After the user specifies an operation, the program should read the numbers from `1.txt` and `2.txt` and apply the operation on each corresponding number from the `1.txt` and `2.txt` files. The results should be stored in the corresponding lines of a new file called `result.txt`.

For example, if the user enters the operator `+`, the numbers in the first lines of `1.txt` and `2.txt` will be added (`925 + 789 = 1714`), and the result will be stored in the first line of a new file called `result.txt`. The same should happen for the remaining lines.


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1. Use <code>File.ReadAllLines</code> to read <code>1.txt</code> and <code>2.txt</code>. <br>
2. <code>StreamWriter</code> will be used in writing the output file.
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  <pre><code class="language-csharp">
using System;

public class Calculator
{
    // Modify these paths if needed
    // These terms are set to 'public' and 'static' to make them accessible for the Unit Tests
    public static string f1Path = "C:\\Users\\Public\\Documents\\1.txt";
    public static string f2Path = "C:\\Users\\Public\\Documents\\2.txt";
    public static string outputPath = "C:\\Users\\Public\\Documents\\result.txt";

    public static void Main(string[] args)
    {
        char opr;

        while (true)
        {
            Console.Write("Enter an operator (+, -, /, *): ");

            // Simplified code using TryParse
            if (char.TryParse(Console.ReadLine(), out opr) && "/-+*".Contains(opr))
                break;

            Console.WriteLine("Invalid operator.");
        }

        // Write code below this line

        string[] numbers_1 = File.ReadAllLines(f1Path);
        string[] numbers_2 = File.ReadAllLines(f2Path);

        float result = 0.0f, n1, n2;
        using (StreamWriter writer = new StreamWriter(outputPath))
        {
            for (int i = 0; i < numbers_1.Length; i++)
            {
                n1 = float.Parse(numbers_1[i]);
                n2 = float.Parse(numbers_2[i]);

                if (opr == '+')
                    result = n1 + n2;
                else if (opr == '-')
                    result = n1 - n2;
                else if (opr == '/')
                    result = n1 / n2;
                else if (opr == '*')
                    result = n1 * n2;

                writer.WriteLine(result);
            }
        }

        Console.WriteLine($"Results saved in {outputPath}");
        // Write code above this line
    }
}
      </code></pre>
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This course will give you a solid foundation to begin making applications using .NET in C#. Covering console applications, asynchronous programming, web services, database fundamentals, and ADO.NET CRUD operations, you'll gain practical skills. From creating apps and handling exceptions to optimizing database access, this course ensures a robust understanding of essential .NET development concepts.

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Challenge: File Based Calculator