C# Console Application display invalid input in while loop

Question

I have this C# console application code here that reads text from a file. when a user inputs a value, it searches the file for lines that contain that value. In my case, the console will ask for a room number, the console will then search room.txt for the room number thats split with ','

class Program
{
    static void Main(string[] args)
    {
        int counter = 0;
        string line;
        string roomNumber;

        Console.WriteLine("Enter room number");
        roomNumber = Console.ReadLine();
        // Read the file and display it line by line.             
        System.IO.StreamReader file = new 
              System.IO.StreamReader("room.txt");
        while ((line = file.ReadLine()) != null)
        {
            string[] words = line.Split(',');
            if (roomNumber == words[1])
            {                 
                Console.WriteLine(line);
            }             
                counter++;
        } 

        file.Close();

        // Suspend the screen.             
         Console.ReadLine(); 
        }
    }
}

How do i make it so that it will write "Invalid room number" when it cant find it in the text file, and then loop back to asking the room number.

this looks an awful lot like a homework assignment...

Timothy Groote
– Timothy Groote

2017-06-06 07:52:41 +00:00
Commented Jun 6, 2017 at 7:52 — Timothy Groote
– Timothy Groote, Commented Jun 6, 2017 at 7:52

Patrick Hofman · Accepted Answer · 2017-06-06 08:31:57Z

3

I would read the entire file at once, construct an enumerable from it and try to find the first match:

bool found = false;

do
{
    Console.WriteLine("Enter room number");
    string roomNumber = Console.ReadLine();

    using (StreamReader file = new StreamReader("room.txt"))
    {
        string str = file.ReadToEnd();
        string[] rooms = str.Split(new char[] { '\r', '\n', ',' }, StringSplitOptions.RemoveEmptyEntries);

        if (!rooms.Any(room => room == roomNumber))
        {
            Console.WriteLine("Invalid room");
        }
        else
        {
            Console.WriteLine($"Found room {roomNumber}");
            found = true;
        }
    }
}
while (!found);

This code uses LINQ to find the first match (Any) on your input array. Then it will display a message if it has found the room or not. Also note the using, which makes your file stream close nicely, even when an exception occurs.

edited Jun 6, 2017 at 8:31

answered Jun 6, 2017 at 7:52

Patrick Hofman

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3 Comments

Patrick Hofman Over a year ago

Any reason to downvote the question and both answers?

jamiedanq Over a year ago

I guess you missed the point where he said he wants to return to the line that asks for the room number after invalid room is displayed

jamiedanq Over a year ago

your answer is better because you use using. Cheers!

Izuka · Accepted Answer · 2017-06-06 08:38:28Z

2

If you want to keep your current code, you can just use a do while loop which will check a boolean specifying if you found a line or not, and exit the loop only when a value is found.

class Program
{
    static void Main(string[] args)
    {
        int counter = 0;
        bool lineFound = false;
        string line;
        string roomNumber;

        do
        {
            Console.WriteLine("Enter room number");
            roomNumber = Console.ReadLine();
            // Read the file and display it line by line.             
            using (StreamReader file = new StreamReader("room.txt"))
            {
                while ((line = file.ReadLine()) != null)
                {
                    string[] words = line.Split(',');
                    if (roomNumber == words[1])
                    {                 
                        Console.WriteLine(line);
                        lineFound = true;
                    }             
                        counter++;
                } 

                if(!lineFound)
                {
                    Console.WriteLine("Invalid room number");
                }
            }

        } while(!lineFound);

        // Suspend the screen.             
         Console.ReadLine(); 
        }
    }
}

edited Jun 6, 2017 at 8:38

answered Jun 6, 2017 at 7:54

Izuka

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1 Comment

Paul Karam Over a year ago

I would suggest using a boolean instead of int as counter here because it makes more sense.

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