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How to make an if loop that loops something until a key is pressed [closed]

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I need to make a loop that loops some console.writeline stuff and does that until the user starts using the keyboard to console.readline(), and enter their own text. So, loop until user types.
Thanks

Not exactly sure what you mean by "loops some console.writeline stuff", but you can use a while loop to write something to the console every x seconds (.5 seconds in the example), and we can use Console.KeyAvailable in the condition, which returns true after the user presses a key:
while (!Console.KeyAvailable)
{
Console.Write(".");
Thread.Sleep(500);
}
Here's one example that displays a "waiting" indicator until the user enters some information:
public static string WaitAndGetUserInput()
{
var chars = new[] {'-', '\\', '|', '/'};
var index = 0;
var left = Console.CursorLeft;
var top = Console.CursorTop;
Console.CursorVisible = false;
while (!Console.KeyAvailable)
{
Console.SetCursorPosition(left, top);
Console.Write(chars[index++ % chars.Length]);
Thread.Sleep(100);
}
var keyPressed = Console.ReadKey(true);
Console.CursorVisible = true;
Console.SetCursorPosition(left, top);
if (keyPressed.Key == ConsoleKey.Enter)
{
Console.Write(' ');
Console.WriteLine();
}
else
{
Console.Write(keyPressed.KeyChar);
}
return keyPressed.Key == ConsoleKey.Enter
? ""
: keyPressed.KeyChar + WaitAndGetUserInput();
}
Sample usage:
public static void Main()
{
Console.Write("Please enter your name: ");
// Display a wait indicator until user enters their name
var userName = WaitAndGetUserInput();
Console.WriteLine($"Welcome, {userName}!");
Console.ReadKey();
}
In the comments you mentioned that you want to flash a ':' after some prompt, and the get user input after that. In order to do this, we can change the code to capture both the ':' position and the cursor position for the user input. By doing this, we can move the cursor to the colon when we need to flash it, and then move it back to the user input location right away.
I also changed it so that it takes in a prompt to display before the user input, and it flashes the last character of that prompt:
public static string FlashLastCharAndGetUserInput(string prompt)
{
if (string.IsNullOrEmpty(prompt)) return Console.ReadLine();
var flash = 0;
var chr = prompt.Last();
// If the last char is a ' ', flash it with a solid block
if (chr == ' ') chr = '▓';
var showChr = false;
var userInput = new StringBuilder();
Console.CursorVisible = false;
Console.Write(prompt);
var colonLeft = Console.CursorLeft - 1;
var colonTop = Console.CursorTop;
var cursorLeft = Console.CursorLeft + 1;
var cursorTop = Console.CursorTop;
while (true)
{
if (++flash % 10000 == 0)
{
Console.SetCursorPosition(colonLeft, colonTop);
Console.Write($"{(showChr ? chr : ' ')} ");
Console.SetCursorPosition(cursorLeft, cursorTop);
showChr = !showChr;
flash = 0;
}
if (!Console.KeyAvailable) continue;
var keyPressed = Console.ReadKey();
if (keyPressed.Key == ConsoleKey.Enter) break;
cursorLeft = Console.CursorLeft;
cursorTop = Console.CursorTop;
if (keyPressed.Key == ConsoleKey.Backspace && userInput.Length > 0)
{
userInput.Remove(userInput.Length - 1, 1);
Console.Write(' ');
Console.SetCursorPosition(cursorLeft, cursorTop);
}
else
{
userInput.Append(keyPressed.KeyChar);
}
}
Console.WriteLine();
return userInput.ToString();
}
In use it would look something like:
public static void Main()
{
var name = FlashLastCharAndGetUserInput("Enter your name:");
Console.WriteLine($"Welcome, {name}");
Console.ReadKey();
}

Decline a string in a string variable

I need to decline the ability to write strings in my console application, at the moment, when text is entered instead of numbers, the console crashes.
I have something along the lines of this right now
class Program
{
static void Main(string[] args)
{
string[] names = new string[2];
string age;
bool agetest = false;
Console.WriteLine("Hello, I am the NameBot2000, What is your first name?");
names[0] = Console.ReadLine();
Console.WriteLine("Well done. What is your surname?");
names[1] = Console.ReadLine();
Console.WriteLine("What year were you born in?");
age = Console.ReadLine();
int.Parse(age);
if (Enumerable.Range(0,2015).Contains(age));
int year = 0;
string wow = "";
if (Enumerable.Range(0,31).Contains(year))
wow = "young";
else if (Enumerable.Range(31,51).Contains(year))
wow = "old";
else if (Enumerable.Range(51,500).Contains(year))
wow = "ancient";
Console.WriteLine("Well done. You said your name was {0} {1}, and you are {2} years old!", names[0], names[1], year);
Console.WriteLine("You are so {0}!", wow);
Console.ReadLine();
}
}
I have tried to incorporate a boolean but I am unsure how to compare the variable to check which format it is in.
Thanks heaps in advance!

Instead of Parse, use TryParse.
int age = 0;
if (Int32.TryParse(Console.Readline, out age)
// Correct format.
else
// error!
What TryParse() will do, is take the user input, Try to Parse it to an int, and if successful, will output an int (and a bool = true), otherwise it will output a bool = false.

use a try catch
string age = console.readline();
bool validage = false;
While(!validage)
{
try
{
int myage = int.parse(age);
validage = true;
}
catch
{
console.write("Please Enter an Integer value for age:");
age = console.readline();
}
}

You can check ConsoleKeyInfo to make sure user can only enter digits for age.
Console.WriteLine("Enter Age : ");
ConsoleKeyInfo key;
string ageStr = "";
do
{
key = Console.ReadKey(true);
if (key.Key != ConsoleKey.Backspace && key.Key != ConsoleKey.Enter)
{
if (char.IsNumber(key.KeyChar))//Check if it is a number
{
ageStr += key.KeyChar;
Console.Write(key.KeyChar);
}
}
else
{
if (key.Key == ConsoleKey.Backspace && ageStr.Length > 0)
{
ageStr = ageStr.Substring(0, (ageStr.Length - 1));
Console.Write("\b \b");
}
}
}
while (key.Key != ConsoleKey.Enter);
Console.WriteLine("Age is {0}", ageStr);

Hide/replace when typing a Password (C#)

Ok, So I am new to C#, but already learned a bit. But I have one question, how do I Replace Characters that are typed into a console with "*" or just hide them completely?
var pw = "eric123";
Console.WriteLine("Password: ");
var value = Console.ReadLine();
if (value == pw)
{
Console.WriteLine("Permitted, Play online? (Y/N)?");
var getGameOnlineStatus = Console.ReadLine();
//Rest Of the Code is just for me :)
Any Help would be appreciated!

found it here
Password masking in C# console application
class PasswordExample
{
static void Main(string[] args)
{
Console.WriteLine("Pls key in your Login ID");
var loginid = Console.ReadLine();
Console.WriteLine("Pls key in your Password");
var password = ReadPassword();
Console.Write("Your Password is:" + password);
Console.ReadLine();
}
public static string ReadPassword()
{
string password = "";
ConsoleKeyInfo info = Console.ReadKey(true);
while (info.Key != ConsoleKey.Enter)
{
if (info.Key != ConsoleKey.Backspace)
{
Console.Write("*");
password += info.KeyChar;
}
else if (info.Key == ConsoleKey.Backspace)
{
if (!string.IsNullOrEmpty(password))
{
// remove one character from the list of password characters
password = password.Substring(0, password.Length - 1);
// get the location of the cursor
int pos = Console.CursorLeft;
// move the cursor to the left by one character
Console.SetCursorPosition(pos - 1, Console.CursorTop);
// replace it with space
Console.Write(" ");
// move the cursor to the left by one character again
Console.SetCursorPosition(pos - 1, Console.CursorTop);
}
}
info = Console.ReadKey(true);
}
// add a new line because user pressed enter at the end of their password
Console.WriteLine();
return password;
}
}

public static string HideCharacter()
{
ConsoleKeyInfo key;
string code = "";
do
{
key = Console.ReadKey(true);
if (Char.IsNumber(key.KeyChar))
{
Console.Write("*");
}
code += key.KeyChar;
} while (key.Key != ConsoleKey.Enter);
return code;
}
password = HideCharacter();

using System;
class Login{
static void Main() {
string passwd = HideCharacter();
Console.WriteLine(passwd);
}
public static string HideCharacter()
{
ConsoleKeyInfo key;
string code = "";
do
{
key = Console.ReadKey(true);
if (Char.IsNumber(key.KeyChar)||Char.IsLetter(key.KeyChar))
{
Console.Write("*");
code += key.KeyChar;
}
} while (key.Key != ConsoleKey.Enter);
return code;
}
}

How do I only allow number input into my C# Console Application?

Console.WriteLine("Enter the cost of the item");
string input = Console.ReadLine();
double price = Convert.ToDouble(input);
Hello, I want the keyboard buttons, A-Z, brackets, question mark, etc to be disabled. I want it so if you type it in, it will not show up in the Console. I only want the numbers 1-9 to show up. This is in C# Console application. Thanks for the help!

try this code snippet
string _val = "";
Console.Write("Enter your value: ");
ConsoleKeyInfo key;
do
{
key = Console.ReadKey(true);
if (key.Key != ConsoleKey.Backspace)
{
double val = 0;
bool _x = double.TryParse(key.KeyChar.ToString(), out val);
if (_x)
{
_val += key.KeyChar;
Console.Write(key.KeyChar);
}
}
else
{
if (key.Key == ConsoleKey.Backspace && _val.Length > 0)
{
_val = _val.Substring(0, (_val.Length - 1));
Console.Write("\b \b");
}
}
}
// Stops Receving Keys Once Enter is Pressed
while (key.Key != ConsoleKey.Enter);
Console.WriteLine();
Console.WriteLine("The Value You entered is : " + _val);
Console.ReadKey();

This MSDN article explains how to read characters one at a time in a console window. Test each character as it is input with the Char.IsNumber() method, and reject those characters that fail the test.

In a while, I got a solution really short:
double number;
Console.Write("Enter the cost of the item: ");
while (!double.TryParse(Console.ReadLine(), out number))
{
Console.Write("This is not valid input. Please enter an integer value: ");
}
Console.Write("The item cost is: {0}", number);
See you!

Here is one approach. It's probably overkill if you're just starting out in C#, since it uses some more advanced aspects of the language. In any case, I hope you find it interesting.
It has some nice features:
The ReadKeys method takes an arbitrary function for testing whether the string so far is valid. This makes it easy to reuse whenever you want filtered input from the keyboard (e.g. letters or numbers but no punctuation).
It should handle anything you throw at it that can be interpreted as a double, e.g. "-123.4E77".
However, unlike John Woo's answer it doesn't handle backspaces.
Here is the code:
using System;
public static class ConsoleExtensions
{
public static void Main()
{
string entry = ConsoleExtensions.ReadKeys(
s => { StringToDouble(s) /* might throw */; return true; });
double result = StringToDouble(entry);
Console.WriteLine();
Console.WriteLine("Result was {0}", result);
}
public static double StringToDouble(string s)
{
try
{
return double.Parse(s);
}
catch (FormatException)
{
// handle trailing E and +/- signs
return double.Parse(s + '0');
}
// anything else will be thrown as an exception
}
public static string ReadKeys(Predicate<string> check)
{
string valid = string.Empty;
while (true)
{
ConsoleKeyInfo key = Console.ReadKey(true);
if (key.Key == ConsoleKey.Enter)
{
return valid;
}
bool isValid = false;
char keyChar = key.KeyChar;
string candidate = valid + keyChar;
try
{
isValid = check(candidate);
}
catch (Exception)
{
// if this raises any sort of exception then the key wasn't valid
// one of the rare cases when catching Exception is reasonable
// (since we really don't care what type it was)
}
if (isValid)
{
Console.Write(keyChar);
valid = candidate;
}
}
}
}
You also could implement an IsStringOrDouble function that returns false instead of throwing an exception, but I leave that as an exercise.
Another way this could be extended would be for ReadKeys to take two Predicate<string> parameters: one to determine whether the substring represented the start of a valid entry and one the second to say whether it was complete. In that way we could allow keypresses to contribute, but disallow the Enter key until entry was complete. This would be useful for things like password entry where you want to ensure a certain strength, or for "yes"/"no" entry.

This code will allow you to:
Write only one dot (because numbers can have only one decimal separator);
One minus at the begining;
One zero at the begining.
It means that you not be able to write something like: "00000.5" or "0000...-5".
class Program
{
static string backValue = "";
static double value;
static ConsoleKeyInfo inputKey;
static void Main(string[] args)
{
Console.Title = "";
Console.Write("Enter your value: ");
do
{
inputKey = Console.ReadKey(true);
if (char.IsDigit(inputKey.KeyChar))
{
if (inputKey.KeyChar == '0')
{
if (!backValue.StartsWith("0") || backValue.Contains('.'))
Write();
}
else
Write();
}
if (inputKey.KeyChar == '-' && backValue.Length == 0 ||
inputKey.KeyChar == '.' && !backValue.Contains(inputKey.KeyChar) &&
backValue.Length > 0)
Write();
if (inputKey.Key == ConsoleKey.Backspace && backValue.Length > 0)
{
backValue = backValue.Substring(0, backValue.Length - 1);
Console.Write("\b \b");
}
} while (inputKey.Key != ConsoleKey.Enter); //Loop until Enter key not pressed
if (double.TryParse(backValue, out value))
Console.Write("\n{0}^2 = {1}", value, Math.Pow(value, 2));
Console.ReadKey();
}
static void Write()
{
backValue += inputKey.KeyChar;
Console.Write(inputKey.KeyChar);
}
}

You can do it with a single line code as follows:
int n;
Console.WriteLine("Enter a number: ");
while (!int.TryParse(Console.ReadLine(), out n)) Console.WriteLine("Integers only allowed."); // This line will do the trick
Console.WriteLine($"The number is {n}");
You can change int into double in case you wanted to allow double instead of integers and so on.

string input;
double price;
bool result = false;
while ( result == false )
{
Console.Write ("\n Enter the cost of the item : ");
input = Console.ReadLine ();
result = double.TryParse (input, out price);
if ( result == false )
{
Console.Write ("\n Please Enter Numbers Only.");
}
else
{
Console.Write ("\n cost of the item : {0} \n ", price);
break;
}
}

Using Readline() and ReadKey() Simultaneously

Is there any way to detect both Readline and ReadKey, so that in most cases it behaves as a readline, except for some special key inputs that should be detected?
I need some "parallel" implementation to introduce simultaneity.
The code below is synchronous and does not meet my need
while ((line = Console.ReadLine()) != "x")
{
if (line == "BLABLA")
{
//Stuff
}
else
{
//Stuff
}
ConsoleKeyInfo ki = Console.ReadKey(true);
if ((ki.Key == ConsoleKey.V) && (ki.Modifiers == ConsoleModifiers.Control))
{
//Stuff
}
}

Here's a function I just made to do this.
Right now it only handles Backspace, Enter and Esc, but it could easily be modified to handle other keys if you deem them necessary.
// returns null if user pressed Escape, or the contents of the line if they pressed Enter.
private static string ReadLineOrEsc()
{
string retString = "";
int curIndex = 0;
do
{
ConsoleKeyInfo readKeyResult = Console.ReadKey(true);
// handle Esc
if (readKeyResult.Key == ConsoleKey.Escape)
{
Console.WriteLine();
return null;
}
// handle Enter
if (readKeyResult.Key == ConsoleKey.Enter)
{
Console.WriteLine();
return retString;
}
// handle backspace
if (readKeyResult.Key == ConsoleKey.Backspace)
{
if (curIndex > 0)
{
retString = retString.Remove(retString.Length - 1);
Console.Write(readKeyResult.KeyChar);
Console.Write(' ');
Console.Write(readKeyResult.KeyChar);
curIndex--;
}
}
else
// handle all other keypresses
{
retString += readKeyResult.KeyChar;
Console.Write(readKeyResult.KeyChar);
curIndex++;
}
}
while (true);
}

No, not as such. Both methods block until the user enters something on the console. So even if you would find a way to have both run in parallel, it will not be deterministic which one gets the first shot.
There is a (not obvious) similar problem: how to make Console.ReadLine() abort/break after a certain amount of time without user input.
There have been multiple attempts for this problem here:
Console.ReadLine Break
How to add a Timeout to Console.ReadLine()?
Most are modelled around either creating your own version of a ReadLine function that adds a timeout (or in your case special handling for certain character (codes)) or the use some sort of threading.
Both ways are either non-trivial or have their own issues (make sure you review the comments, even for the accepted answers).
In short, I think you will need to roll your own version of ReadLine, based on Console.ReadKey with your special handling included and that much of the genuine Console.ReadLine behavior that you require. Note that this even include such basic things as RETURN, ARROW KEYS, BACKSPACE handling, etc.
Update: There is the getline.cs Code from the Mono project, which implements a line editing capability like it was provided by some venerable UNIX shells (EMACS mode, if you care). For that, I believe it will need to implement some sort of ReadLine replacement, although I haven't checked. Maybe you can use this as a starting point.

Here is a method that I created that works great. You do not have to press button twice in order for string to start appearing. Basically this replaces Console.ReadLine() but it also looks for Esc key pressed. Just look at return type of method if it is null then you know Esc was pressed.
private string ReadLineOrEscape()
{
ConsoleKeyInfo keyInfo = new ConsoleKeyInfo();
StringBuilder sb = new StringBuilder();
int index = 0;
while (keyInfo.Key != ConsoleKey.Enter)
{
keyInfo = Console.ReadKey(true);
if (keyInfo.Key == ConsoleKey.Escape)
{
return null;
}
if(keyInfo.Key == ConsoleKey.Backspace)
{
if (index > 0)
{
Console.CursorLeft = index - 1;
sb.Remove(index - 1, 1);
Console.Write(" \b");
index--;
}
}
if(keyInfo.KeyChar > 31 && keyInfo.KeyChar < 127)
{
index++;
Console.Write(keyInfo.KeyChar);
sb.Append(keyInfo.KeyChar);
}
}
return sb.ToString(); ;
}

In response to #Overlord Zurd, I improved the code provided by the user.
public class ConsoleOutput
{
private ConsoleOutputType OutputType { get; set; }
private object MyObject { get; }
private static bool IsInserting { get; set; }
public string KeyName => IsKey() && (ConsoleKeyInfo)MyObject != null ? ((ConsoleKeyInfo)MyObject).Key.ToString() : "Null";
public string OutputString => !IsKey() && MyObject != null ? (string)MyObject : string.Empty;
public static event Action<string> ReadInput = delegate { };
public static event Action<ConsoleKeyInfo> ReadKey = delegate { };
private ConsoleOutput()
{
}
public ConsoleOutput(object obj)
{
MyObject = obj;
OutputType = obj is ConsoleKeyInfo ? ConsoleOutputType.Key : ConsoleOutputType.Value;
}
public bool IsKey()
{
return OutputType == ConsoleOutputType.Key;
}
public bool IsExitKey()
{
if (!IsKey())
return false;
var info = ((ConsoleKeyInfo)MyObject);
return (info.Modifiers & ConsoleModifiers.Control) != 0 && info.Key == ConsoleKey.B;
}
public string GetValue()
{
return (string)MyObject;
}
// returns null if user pressed Escape, or the contents of the line if they pressed Enter.
public static ConsoleOutput ReadLineOrKey()
{
string retString = "";
int curIndex = 0;
do
{
ConsoleKeyInfo readKeyResult = Console.ReadKey(true);
// handle Enter
if (readKeyResult.Key == ConsoleKey.Enter)
{
ReadInput?.Invoke(retString);
Console.WriteLine();
return new ConsoleOutput(retString);
}
// handle backspace
if (readKeyResult.Key == ConsoleKey.Backspace)
{
if (curIndex > 0)
{
retString = retString.Remove(retString.Length - 1);
Console.Write(readKeyResult.KeyChar);
Console.Write(' ');
Console.Write(readKeyResult.KeyChar);
--curIndex;
}
}
else if (readKeyResult.Key == ConsoleKey.Delete)
{
if (retString.Length - curIndex > 0)
{
// Store current position
int curLeftPos = Console.CursorLeft;
// Redraw string
for (int i = curIndex + 1; i < retString.Length; ++i)
Console.Write(retString[i]);
// Remove last repeated char
Console.Write(' ');
// Restore position
Console.SetCursorPosition(curLeftPos, Console.CursorTop);
// Remove string
retString = retString.Remove(curIndex, 1);
}
}
else if (readKeyResult.Key == ConsoleKey.RightArrow)
{
if (curIndex < retString.Length)
{
++Console.CursorLeft;
++curIndex;
}
}
else if (readKeyResult.Key == ConsoleKey.LeftArrow)
{
if (curIndex > 0)
{
--Console.CursorLeft;
--curIndex;
}
}
else if (readKeyResult.Key == ConsoleKey.Insert)
{
IsInserting = !IsInserting;
}
#if DEBUG
else if (readKeyResult.Key == ConsoleKey.UpArrow)
{
if (Console.CursorTop > 0)
--Console.CursorTop;
}
else if (readKeyResult.Key == ConsoleKey.DownArrow)
{
if (Console.CursorTop < Console.BufferHeight - 1)
++Console.CursorTop;
}
#endif
else
// handle all other keypresses
{
if (IsInserting || curIndex == retString.Length)
{
retString += readKeyResult.KeyChar;
Console.Write(readKeyResult.KeyChar);
++curIndex;
}
else
{
// Store char
char c = readKeyResult.KeyChar;
// Write char at position
Console.Write(c);
// Store cursor position
int curLeftPos = Console.CursorLeft;
// Clear console from curIndex to end
for (int i = curIndex; i < retString.Length; ++i)
Console.Write(' ');
// Go back
Console.SetCursorPosition(curLeftPos, Console.CursorTop);
// Write the chars from curIndex to end (with the new appended char)
for (int i = curIndex; i < retString.Length; ++i)
Console.Write(retString[i]);
// Restore again
Console.SetCursorPosition(curLeftPos, Console.CursorTop);
// Store in the string
retString = retString.Insert(curIndex, new string(c, 1));
// Sum one to the cur index (we appended one char)
++curIndex;
}
}
if (char.IsControl(readKeyResult.KeyChar) &&
readKeyResult.Key != ConsoleKey.Enter &&
readKeyResult.Key != ConsoleKey.Backspace &&
readKeyResult.Key != ConsoleKey.Tab &&
readKeyResult.Key != ConsoleKey.Delete &&
readKeyResult.Key != ConsoleKey.RightArrow &&
readKeyResult.Key != ConsoleKey.LeftArrow &&
readKeyResult.Key != ConsoleKey.Insert)
{
#if DEBUG
if (readKeyResult.Key == ConsoleKey.UpArrow || readKeyResult.Key == ConsoleKey.DownArrow)
continue;
#endif
ReadKey?.Invoke(readKeyResult);
Console.WriteLine();
return new ConsoleOutput(readKeyResult);
}
}
while (true);
}
}
As you can see, I implemented Insert, Arrow control, Delete, etc etc... (Insert was an important thing because if you write any text with this code you will see behavior as Insert key provides).
And example of use:
internal class Program
{
private static void Main(string[] args)
{
Console.Write("Write test string: ");
var test = ConsoleOutput.ReadLineOrKey();
if (test.IsKey())
Console.WriteLine(test.KeyName);
else
Console.WriteLine($"Output string: {test.OutputString}");
Console.Read();
}
}
You can keep updated on this link (is a link to my lib I'm currently working at).