Develop Reference

Trying to make a menu that keeps repeating if the user enters something invalid

Total beginner here, literally started learning programming for the first time in my life yesterday, so please don't judge!
I'm trying to make a program that allows the user to enter the name and score of videogames, then show these scores upon request. I'm trying to make a menu. I noticed the program would crash if the user presses enter without entering any number, and I wanted to avoid that, but I'm stuck. If I press enter it doesn't crash. However, if I enter 1 or 2, the menu keeps going anyways, and if I press enter without entering anything after that, then it crashes? I'm lost.
namespace videogaems
{
class Program
{
static void Main(string[] args)
{
menu();
}
static void menu()
{
int option = 0;
Console.WriteLine("Select what you want to do: ");
Console.WriteLine("1- add game");
Console.WriteLine("2- show game rating");
bool tryAgain = true;
while (tryAgain)
{
try
{
while (option != 1 || option != 2)
{
option = Convert.ToInt32(Console.ReadLine());
tryAgain = false;
}
}
catch (FormatException)
{
option = 0;
}
}
}

Convert.ToInt32(Console.ReadLine()) will throw an exception if the string cannot be converted to an integer. Instead, you should use int.TryParse, which takes in a string and an out parameter that gets set to the converted value (if successful). It returns a bool which indicates if it was successful or not.
For example, the following code will loop as long as int.TryParse fails, and when it succeeds, userInput will contain the converted number:
int userInput;
while (!int.TryParse(Console.ReadLine(), out userInput))
{
Console.WriteLine("Please enter a whole number");
}
Another option, however, is to simply use Console.ReadKey(), which returns a ConsoleKeyInfo object that represents the key that the user pressed. Then we can just check the value of the key character (and ignore any keys that are invalid).
For example:
static void Menu()
{
bool exit = false;
while (!exit)
{
Console.Clear();
Console.WriteLine("Select what you want to do: ");
Console.WriteLine(" 1: Add a game");
Console.WriteLine(" 2: Show game rating");
Console.WriteLine(" 3: Exit");
ConsoleKeyInfo userInput = Console.ReadKey();
Console.WriteLine();
switch (userInput.KeyChar)
{
case '1':
// Code to add a game goes here (call AddGame() method, for example)
Console.Clear();
Console.WriteLine("Add a game was selected");
Console.WriteLine("Press any key to return to menu");
Console.ReadKey();
break;
case '2':
// Code to show a game rating goes here (call ShowRating(), for example)
Console.Clear();
Console.WriteLine("Show game rating was selected");
Console.WriteLine("Press any key to return to menu");
Console.ReadKey();
break;
case '3':
// Exit the menu
exit = true;
break;
}
}
}

How to make the program read the enter key and stop the loop?

I want to make a little game. The program will output numbers in a loop, and the person has to stop the loop in the exact number that was specified before, by clicking the 'enter' key. like so:
static void Main(string[] args)
{
Console.WriteLine("try to click the 'enter' button when the program shows the number 4");
for (int i = 0; i < 10; i++)
{
Console.WriteLine(i);
//here will be the command which reads the enter key and stops the loop
}
}
One of the users told me to use this code:
Console.WriteLine("try to click the 'enter' button when the program shows the number 4");
for (int i = 0; i < 10; i++)
{
Console.WriteLine(i);
if (e.KeyChar == (char)13)
{
break;
}
}
The problem is, when i use this code, i have an error which says 'the name 'e' does not exist in the current context'.
What does that mean?
Thanks in advance.

There are two basic methods for reading console input:
Console.ReadLine() will pause and wait for the user to enter text followed by the enter key, returning everything entered before the enter key is pressed as a string.
Console.ReadKey() will wait for a keypress and return it as a ConsoleKeyInfo structure with information on the key pressed, what character (if any) it represents and what modifier keys (ctrl, alt, shift) were pressed.
If you don't want to wait until the user presses a key you can use the Console.KeyAvailable property to check if there is a keypress waiting to be read. This can be used in a timing loop to provide a timeout for key entry:
DateTime endTime = DateTime.Now.AddSeconds(10);
while (DateTime.Now < endTime)
{
if (Console.KeyAvailable)
{
var key = Console.ReadKey();
if (key.Key == ConsoleKey.Enter)
{
// do something with key
//...
// stop waiting
break;
}
}
// sleep to stop your program using all available CPU
Thread.Sleep(0);
}

I found a basic idea for a solution to your problem here.
In this answer he is using the Console.KeyAvaliable property to check if a Key has been pressed and then checks if the press key is the one you are lookig for.
To fit it to your needs you have to change it like so:
static void Main (string[] args)
{
Console.WriteLine ("try to click the 'enter' button when the program shows the number 4");
int counter = 0;
int limit = 100000;
do {
while (counter < limit && !Console.KeyAvailable) {
Console.WriteLine (counter);
counter++;
}
} while (Console.ReadKey (true).Key != ConsoleKey.Enter);
}

Try:
ConsoleKeyInfo cki;
do
{
cki = Console.ReadKey();
//What you need to do code
} while (cki.Key != ConsoleKey.Enter);
Console.ReadKey() will wait for a keypress and return it as a ConsoleKey, you just catch and test if it's your desired key.

Yes/No Menu Using Characters Doesn't Work Correctly

I'm trying to make a simple menu where you select one option or the other to proceed. Instead of "yes" or "no" this menu uses "read" or "write" as the two options but the concept is of course the same. The code looks like this...
public void Start()
{
char selection;
do
{
Console.WriteLine("Would you like to read (r) or write (w) to a file?");
selection = (char) Console.Read();
} while (selection != 'r' || selection != 'w');
}
Now not only does this not stop looping when you DO type in either 'r' or 'w' but it types out 3 lines of the WriteLine text after you press enter anytime after.
Can anyone shed some light on how to fix this? I'm assuming I'm improperly using the Read() method but being the newbie that I am I find it hard to simply trial and error my way through some things. Any help at all would be amazing. Thank you in advance.
EDIT
public void Start()
{
char selection = 'y';
while(selection == 'y')
{
Console.Write("Would you like to continue...");
selection = (char)Console.Read();
Flush();
}
}
public void Flush()
{
while(Console.In.Peek() != -1)
{
Console.In.Read();
}
}

selection != 'r' || selection != 'w' is always true. If selection is r, then the selection != 'w' part is true, and if selection is not r, then the selection != 'r' part is true, so you either have false || true (which is true), or true || ... (the latter operand doesn't matter) which is also true.
You probably want while (selection != 'r' && selection != 'w').

Console.Read() will give you the characters as they are typed. As soon as they type the 'r' is stops. Isn't that what you want?
Hitting ENTER actually generates 2 characters, so it will print out the prompt 2 more times.
Maybe you just want this:
public void Start()
{
char selection;
Console.WriteLine("Would you like to read (r) or write (w) to a file?");
do
{
selection = (char) Console.Read();
} while (selection != 'r' && selection != 'w');
}

Another way to resolve your question is break the loop with a break call and then return the inserted value.
Example:
class Program
{
static void Main(string[] args)
{
char selection = read_or_write();
Console.WriteLine("char in main function: "+selection);
Console.WriteLine("press enter to close");
Console.ReadLine(); //clean with enter keyboard
}
public static char read_or_write()
{
char selection;
Console.WriteLine("Would you like to read (r) or write (w) to a file?");
do
{
selection = (char)Console.Read();
Console.ReadLine();//clean with enter keyboard
if (selection == 'r')
{
Console.WriteLine("You pressed r");
break;
}
else if (selection == 'w')
{
Console.WriteLine("You pressed w");
break;
}
else
{
Console.WriteLine("You pressed a wrong key!");
}
} while (selection != 'r' || selection != 'w');
return selection;
}
}

C#, how do I close my app by pressing the "Enter" button?

I'm new to C# and was wondering, if I wanted to close my app by pressing the Enter button how would I do so? After doing some research on this website the closest thing I found to doing the trick is this code,
string key = Console.ReadKey().ToString();
if (key == "")
{
Console.WriteLine("User pressed enter!");
return;
}
However, this doesn't do what I want it to. For this, if I press Enter it just takes to to the "press any button to close this app". If anyone could help that would be great.
Thanks.

In some cases it's enough to place Console.ReadLine() at the end of the Main method:
static void Main(string[] args) {
// your code here
Console.ReadLine();
}

Is your application a Console Application? Or is it a Windows Forms Application?
For a Console Application, which by default closes automatically at the conclusion of execution, we would need to prevent the application from closing until the user presses the Enter key. This can be done easily using the following code:
ConsoleKeyInfo keyInfo;
do { keyInfo = Console.ReadKey(true); }
while (keyInfo.Key != ConsoleKey.Enter);
For a Windows Forms Application, a different approach is required. We would need to intercept the Enter key when the user presses it and close the form, which will exit the application if it is the main form. We can accomplish via the KeyUp() event of the form:
private void MainForm_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
this.Close();
}
}
The event handler can be added from the designer, or from code using the following statement:
this.KeyUp += MainForm_KeyUp;
Finally, in order listen to key events regardless of what control on the form has focus, we need to set the KeyPreview property of the form to true, which can be done within the designer, or in code as follows:
public MainForm()
{
InitializeComponent();
// Set KeyPreview property to listen for key events:
this.KeyPreview = true;
}

I'm going to assume it is a console application.
This is the way I do it:
Use a 'while'-loop and break when wanting to stop
Explained with some code:
static void Main(string[] args)
{
while (true)
{
Console.WriteLine("test");
ConsoleKeyInfo key = Console.ReadKey();
if (key.Key == ConsoleKey.Enter) break;
else Console.WriteLine("You gave something else");
Console.WriteLine("This is the end of the app");
break;
}
}

Google is your friend. The answer is a simple modification to your if statement of ConsoleKey.Enter as seen here:
public static void Main()
{
DateTime dat = DateTime.Now;
Console.WriteLine("The time: {0:d} at {0:t}", dat);
TimeZoneInfo tz = TimeZoneInfo.Local;
Console.WriteLine("The time zone: {0}\n",
tz.IsDaylightSavingTime(dat) ?
tz.DaylightName : tz.StandardName);
Console.Write("Press <Enter> to exit... ");
while (Console.ReadKey().Key != ConsoleKey.Enter) {} // <-- check for enter key
}
Original information here

Detecting key presses in console [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
how to handle key press event in console application
a simple question.
I am writing a simple text based adventure game for fun and I am stuck on the first part already! How can I make my console check for key presses I.E: press enter to continue!

You can use
Console.ReadKey();
To read 1 key. You could then do something like this:
string key = Console.ReadKey().Key.ToString();
if(key.ToUpper() == "W")
Console.WriteLine("User typed 'W'!");
else
Console.WriteLine("User did not type 'W'");
Or:
if(key == "")
Console.WriteLine("User pressed enter!");
else
Console.WriteLine("User did not press enter.");
And if you do not care if the user types anything but presses enter after, you could just do:
// Some code here
Console.ReadLine();
// Code here will be run after they press enter

The Console class contains all the methods needed to read and write to the 'console'
For example
Console.Write("Press Enter to continue!")
do
{
ConsoleKeyInfo c = Console.ReadKey();
} while (c.Key != ConsoleKey.Enter);

Console.Write("Press Enter to continue!")
Console.ReadLine();
The program will not continue until the user hits Enter.
You can also check for other specific keys using Console.ReadKey:
void WaitForKey(ConsoleKey key)
{
while (Console.ReadKey(true).Key != key)
{ }
}
Usage:
Console.Write("Press 'Y' to continue.");
WaitForKey(ConsoleKey.Y);

An event, that would do it.
private void OnKeyDownHandler(object sender, KeyEventArgs e)
{
if (e.Key == Key.Return)
{
Console.Write("Press Enter to continue!")
}
}