I am trying to create a static method that validates if input is actually a number or not and I want to do it with a regex. I get an error "cannot convert int to string" when I try to do it, but it's my understanding that integers also can be compared using regex.
This is my static method so far.
public static void validatenumber(int number)
{
Regex regex = new Regex("^[0-9]+$");
if (regex.IsMatch(number))
{
Console.WriteLine("The input is a number");
}
else
{
Console.WriteLine("The input is not a number");
}
}
And this is the input that I am trying to validate, which is in the Main method.
Console.WriteLine("Please enter a number");
int number= Convert.ToInt32(Console.ReadLine());
validatenumber(number);
My variable number in my Main method needs to be an int, I cannot change that.
Your problem is not the Regex error you are getting, but the fact that you are trying to validate an int as a number. There is no sense in this validation, since the compiler will never allow an int variable to hold something else except a number.
It would make sense if yot method was receiving a string as a parameter:
validatenumber(string number)
In which case, you would not get this error, since Regex works with strings.
An issue with you code is found here, which leads to your regex (as you have to perform regex on a string not an int).
Console.WriteLine("Please enter a number");
int number= Convert.ToInt32(Console.ReadLine()); // <--- Here!
validatenumber(number);
Console.ReadLine() will return a string. So your code will throw an error or give you an unexpected result when you try to do Convert.ToInt32() on it.
You will need to change your code to look like the following:
static void Main(string[] args)
{
...
Console.WriteLine("Please enter a number");
string numberString = Console.ReadLine();
int number = ConvertAndValidateNumber(number); // we are now going to return an int
...
}
and then change the the validatenumber method to return the int type using the int.TryParse() method, which is much easier to read.
public static int ConvertAndValidateNumber(string numberString)
{
int.TryParse(numberString, out int number);
return number;
}
If you REALLY want to use RegEx (which makes sense in some very special cases), then you can change the above method to:
public static int ConvertAndValidateNumberUsingRegEx(string numberString)
{
int number;
//
// put your RegEx here...
//
// and don't forget to assign the converted string value into the number
number = (your converted string);
// return it
return number;
}
You also may want to validate that your regex is valid by testing it here http://regexr.com/
Related
This is only a small piece of the code I'm trying to make work. The original code I wrote works but I want to make sure when the user inputs a number it is in fact a number.
Console.WriteLine("Give the number of A");
A =Convert.ToDouble( Console.ReadLine());
if (char.IsNumber(Convert.ToDouble(A)) == correct)
{
Console.WriteLine(Convert.ToDouble( A * A));
}
else
{
Console.WriteLine("Incorrecrt input");
}
The Console.WriteLine(Convert.ToDouble(A*A)); I only wrote to see if that will work and it doesn't. After the user inputs only a number I must use it in another equation for a final answer. The user must input 3 numbers.
For me, you should check is the input is a number that you can convert to double before converting it.
Console.WriteLine("Give the number of A");
var a = Console.ReadLine();
double number;
if (double.TryParse(a, out number))//double.TryParse takes a parameter and tries to convert it to double. If the convertion is successfull, sets the out parameter as result and returns true. If not, returns false. And you can use with other types like int.Tryparse(param, out outParam);
{
A = number;
}
else
{
//Not a number, show a message etc...
{
If you break this down:
A =Convert.ToDouble( Console.ReadLine());
if (char.IsNumber(Convert.ToDouble(A)) == correct)
{
}
What you're basically doing is:
Double A = Convert.ToDouble(Console.ReadLine());
Double dbl = Convert.ToDouble(A);
Boolean bl = char.IsNumber(dbl);
if (bl== correct)
{
}
So there's multiple things wrong here.
Firstly, you're trying to convert the user input without any sort of guarantee of success, so if someone typed "A" instead of a number it will throw an exception.
You should use TryParse and then if it's a valid conversion proceed.
Secondly, you're checking if a Double is a char that can be converted to a number. Obviously not because it's already a Double.
Thirdly, you're checking if a Boolean is equal to some variable called correct (which you haven't provided the definition of) so it's not clear if this is a valid comparsion.
EDIT:
This is what I would do:
bool validInput = false;
do
{
Console.WriteLine("Give the number of A");
string userInput = Console.ReadLine();
if (double.TryParse(userInput, out double result))
{
validInput = true;
Console.WriteLine(result * result);
Console.ReadLine();
}
else
{
Console.WriteLine("Invalid input. Please type a number.");
}
} while (!validInput);
I couldn't find any c# examples in the 30 seconds I spent looking for one, but I have a problem. When a user types a string instead of an integer the console crashes and I cannot for the life of me handle this exception.
static void Main(string[] args)
{
Console.Write("Age: ");
int Age = Convert.ToInt32(Console.ReadLine());
Console.ReadKey();
}
you are casting whatever user has typed in console to integer by Convert.ToInt32 without checking whatever user has typed is actaully valid number string or any other alphanumeric string (or pure aplhabatic or special charactors)
you must make sure that user's input is valid numeric or not while casting.
you can use TryParse instead of Convert.ToInt32 for that. like below,
int.TryParse(Console.ReadLine(), out Age);
more interesting, this method returns a boolean too. if conversion is succssfull then it will return true else false. So if your further logic is depandant on Age you can prevent it from performing if user has not entered valid input.
like below.
while(true)
{
if (int.TryParse(Console.ReadLine(), out Age))
{
break;
}
else
{
Console.WriteLine("Invalid input for age, please enter again");
}
}
//from here your further logic
I too find for solution for 30 seconds on google, surprisingly i found lot of interesting links
Google
MSDN
https://stackify.com/convert-csharp-string-int/
Is there a try Convert.ToInt32... avoiding exceptions
static void Main(string[] args)
{
Try{
Console.Write("Age: ");
int Age = Convert.ToInt32(Console.ReadLine());
Console.ReadKey();
}
Catch (Exception e){
Console.writeLine(e)
}
}
What I am looking for is how to read an integer that was given by the user from the command line (console project). I primarily know C++ and have started down the C# path. I know that Console.ReadLine(); only takes a char/string. So in short I am looking for the integer version of this.
Just to give you an idea of what I'm doing exactly:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
Console.ReadLine(); // Needs to take in int rather than string or char.
I have been looking for quite a while for this. I have found a lot on C but not C#. I did find however a thread, on another site, that suggested to convert from char to int. I'm sure there has to be a more direct way than converting.
You can convert the string to integer using Convert.ToInt32() function
int intTemp = Convert.ToInt32(Console.ReadLine());
I would suggest you use TryParse:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
string input = Console.ReadLine();
int number;
Int32.TryParse(input, out number);
This way, your application does not throw an exception, if you try to parse something like "1q" or "23e", because somebody made a faulty input.
Int32.TryParse returns a boolean value, so you can use it in an if statement, to see whether or not you need to branch of your code:
int number;
if(!Int32.TryParse(input, out number))
{
//no, not able to parse, repeat, throw exception, use fallback value?
}
To your question: You will not find a solution to read an integer because ReadLine() reads the whole command line, threfor returns a string. What you can do is, try to convert this input into and int16/32/64 variable.
There are several methods for this:
Int.Parse()
Convert.ToInt()
Int.TryParse()
If you are in doubt about the input, which is to be converted, always go for the TryParse methods, no matter if you try to parse strings, int variable or what not.
Update
In C# 7.0 out variables can be declared directly where they are passed in as an argument, so the above code could be condensed into this:
if(Int32.TryParse(input, out int number))
{
/* Yes input could be parsed and we can now use number in this code block
scope */
}
else
{
/* No, input could not be parsed to an integer */
}
A complete example would look like this:
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
var foo = Console.ReadLine();
if (int.TryParse(foo, out int number1)) {
Console.WriteLine($"{number1} is a number");
}
else
{
Console.WriteLine($"{foo} is not a number");
}
Console.WriteLine($"The value of the variable {nameof(number1)} is {number1}");
Console.ReadLine();
}
}
Here you can see, that the variable number1 does get initialized even if the input is not a number and has the value 0 regardless, so it is valid even outside the declaring if block
You need to typecast the input. try using the following
int input = Convert.ToInt32(Console.ReadLine());
It will throw exception if the value is non-numeric.
Edit
I understand that the above is a quick one. I would like to improve my answer:
String input = Console.ReadLine();
int selectedOption;
if(int.TryParse(input, out selectedOption))
{
switch(selectedOption)
{
case 1:
//your code here.
break;
case 2:
//another one.
break;
//. and so on, default..
}
}
else
{
//print error indicating non-numeric input is unsupported or something more meaningful.
}
int op = 0;
string in = string.Empty;
do
{
Console.WriteLine("enter choice");
in = Console.ReadLine();
} while (!int.TryParse(in, out op));
Use this simple line:
int x = int.Parse(Console.ReadLine());
I didn't see a good and complete answer to your question, so I will show a more complete example. There are some methods posted showing how to get integer input from the user, but whenever you do this you usually also need to
validate the input
display an error message if invalid input
is given, and
loop through until a valid input is given.
This example shows how to get an integer value from the user that is equal to or greater than 1. If invalid input is given, it will catch the error, display an error message, and request the user to try again for a correct input.
static void Main(string[] args)
{
int intUserInput = 0;
bool validUserInput = false;
while (validUserInput == false)
{
try
{
Console.Write("Please enter an integer value greater than or equal to 1: ");
intUserInput = int.Parse(Console.ReadLine()); //try to parse the user input to an int variable
}
catch (Exception e) //catch exception for invalid input, such as a letter
{
Console.WriteLine(e.Message);
}
if (intUserInput >= 1) { validUserInput = true; }
else { Console.WriteLine(intUserInput + " is not a valid input, please enter an integer greater than 0."); }
} //end while
Console.WriteLine("You entered " + intUserInput);
Console.WriteLine("Press any key to exit ");
Console.ReadKey();
} //end main
In your question it looks like you wanted to use this for menu options. So if you wanted to get int input for choosing a menu option you could change the if statement to
if ( (intUserInput >= 1) && (intUserInput <= 4) )
This would work if you needed the user to pick an option of 1, 2, 3, or 4.
I used int intTemp = Convert.ToInt32(Console.ReadLine()); and it worked well, here's my example:
int balance = 10000;
int retrieve = 0;
Console.Write("Hello, write the amount you want to retrieve: ");
retrieve = Convert.ToInt32(Console.ReadLine());
Better way is to use TryParse:
Int32 _userInput;
if(Int32.TryParse (Console.Readline(), out _userInput) {// do the stuff on userInput}
Try this it will not throw exception and user can try again:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice = 0;
while (!Int32.TryParse(Console.ReadLine(), out choice))
{
Console.WriteLine("Wrong input! Enter choice number again:");
}
static void Main(string[] args)
{
Console.WriteLine("Please enter a number from 1 to 10");
int counter = Convert.ToInt32(Console.ReadLine());
//Here is your variable
Console.WriteLine("The numbers start from");
do
{
counter++;
Console.Write(counter + ", ");
} while (counter < 100);
Console.ReadKey();
}
You could create your own ReadInt function, that only allows numbers
(this function is probably not the best way to go about this, but does the job)
public static int ReadInt()
{
string allowedChars = "0123456789";
ConsoleKeyInfo read = new ConsoleKeyInfo();
List<char> outInt = new List<char>();
while(!(read.Key == ConsoleKey.Enter && outInt.Count > 0))
{
read = Console.ReadKey(true);
if (allowedChars.Contains(read.KeyChar.ToString()))
{
outInt.Add(read.KeyChar);
Console.Write(read.KeyChar.ToString());
}
if(read.Key == ConsoleKey.Backspace)
{
if(outInt.Count > 0)
{
outInt.RemoveAt(outInt.Count - 1);
Console.CursorLeft--;
Console.Write(" ");
Console.CursorLeft--;
}
}
}
Console.SetCursorPosition(0, Console.CursorTop + 1);
return int.Parse(new string(outInt.ToArray()));
}
Declare a variable that will contain the value of the user input :
Ex :
int userInput = Convert.ToInt32(Console.ReadLine());
I know this question is old, but with some newer C# features like lambda expressions, here's what I actually implemented for my project today:
private static async Task Main()
{
// -- More of my code here
Console.WriteLine("1. Add account.");
Console.WriteLine("2. View accounts.");
int choice = ReadInt("Please enter your choice: ");
// -- Code that uses the choice variable
}
// I have this as a public function in a utility class,
// but you could use it directly in Program.cs
private static int ReadInt(string prompt)
{
string? text;
do
{
Console.Write(prompt);
text = Console.ReadLine();
} while (text == null || !text.Where(c => char.IsNumber(c)).Any());
return int.Parse(new string(text.Where(c => char.IsNumber(c)).ToArray()));
}
The difference here is that if you accidentally type a number and any other text along with that number, only the number is parsed.
You could just go ahead and try :
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice=int.Parse(Console.ReadLine());
That should work for the case statement.
It works with the switch statement and doesn't throw an exception.
What I am looking for is how to read an integer that was given by the user from the command line (console project). I primarily know C++ and have started down the C# path. I know that Console.ReadLine(); only takes a char/string. So in short I am looking for the integer version of this.
Just to give you an idea of what I'm doing exactly:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
Console.ReadLine(); // Needs to take in int rather than string or char.
I have been looking for quite a while for this. I have found a lot on C but not C#. I did find however a thread, on another site, that suggested to convert from char to int. I'm sure there has to be a more direct way than converting.
You can convert the string to integer using Convert.ToInt32() function
int intTemp = Convert.ToInt32(Console.ReadLine());
I would suggest you use TryParse:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
string input = Console.ReadLine();
int number;
Int32.TryParse(input, out number);
This way, your application does not throw an exception, if you try to parse something like "1q" or "23e", because somebody made a faulty input.
Int32.TryParse returns a boolean value, so you can use it in an if statement, to see whether or not you need to branch of your code:
int number;
if(!Int32.TryParse(input, out number))
{
//no, not able to parse, repeat, throw exception, use fallback value?
}
To your question: You will not find a solution to read an integer because ReadLine() reads the whole command line, threfor returns a string. What you can do is, try to convert this input into and int16/32/64 variable.
There are several methods for this:
Int.Parse()
Convert.ToInt()
Int.TryParse()
If you are in doubt about the input, which is to be converted, always go for the TryParse methods, no matter if you try to parse strings, int variable or what not.
Update
In C# 7.0 out variables can be declared directly where they are passed in as an argument, so the above code could be condensed into this:
if(Int32.TryParse(input, out int number))
{
/* Yes input could be parsed and we can now use number in this code block
scope */
}
else
{
/* No, input could not be parsed to an integer */
}
A complete example would look like this:
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
var foo = Console.ReadLine();
if (int.TryParse(foo, out int number1)) {
Console.WriteLine($"{number1} is a number");
}
else
{
Console.WriteLine($"{foo} is not a number");
}
Console.WriteLine($"The value of the variable {nameof(number1)} is {number1}");
Console.ReadLine();
}
}
Here you can see, that the variable number1 does get initialized even if the input is not a number and has the value 0 regardless, so it is valid even outside the declaring if block
You need to typecast the input. try using the following
int input = Convert.ToInt32(Console.ReadLine());
It will throw exception if the value is non-numeric.
Edit
I understand that the above is a quick one. I would like to improve my answer:
String input = Console.ReadLine();
int selectedOption;
if(int.TryParse(input, out selectedOption))
{
switch(selectedOption)
{
case 1:
//your code here.
break;
case 2:
//another one.
break;
//. and so on, default..
}
}
else
{
//print error indicating non-numeric input is unsupported or something more meaningful.
}
int op = 0;
string in = string.Empty;
do
{
Console.WriteLine("enter choice");
in = Console.ReadLine();
} while (!int.TryParse(in, out op));
Use this simple line:
int x = int.Parse(Console.ReadLine());
I didn't see a good and complete answer to your question, so I will show a more complete example. There are some methods posted showing how to get integer input from the user, but whenever you do this you usually also need to
validate the input
display an error message if invalid input
is given, and
loop through until a valid input is given.
This example shows how to get an integer value from the user that is equal to or greater than 1. If invalid input is given, it will catch the error, display an error message, and request the user to try again for a correct input.
static void Main(string[] args)
{
int intUserInput = 0;
bool validUserInput = false;
while (validUserInput == false)
{
try
{
Console.Write("Please enter an integer value greater than or equal to 1: ");
intUserInput = int.Parse(Console.ReadLine()); //try to parse the user input to an int variable
}
catch (Exception e) //catch exception for invalid input, such as a letter
{
Console.WriteLine(e.Message);
}
if (intUserInput >= 1) { validUserInput = true; }
else { Console.WriteLine(intUserInput + " is not a valid input, please enter an integer greater than 0."); }
} //end while
Console.WriteLine("You entered " + intUserInput);
Console.WriteLine("Press any key to exit ");
Console.ReadKey();
} //end main
In your question it looks like you wanted to use this for menu options. So if you wanted to get int input for choosing a menu option you could change the if statement to
if ( (intUserInput >= 1) && (intUserInput <= 4) )
This would work if you needed the user to pick an option of 1, 2, 3, or 4.
I used int intTemp = Convert.ToInt32(Console.ReadLine()); and it worked well, here's my example:
int balance = 10000;
int retrieve = 0;
Console.Write("Hello, write the amount you want to retrieve: ");
retrieve = Convert.ToInt32(Console.ReadLine());
Better way is to use TryParse:
Int32 _userInput;
if(Int32.TryParse (Console.Readline(), out _userInput) {// do the stuff on userInput}
Try this it will not throw exception and user can try again:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice = 0;
while (!Int32.TryParse(Console.ReadLine(), out choice))
{
Console.WriteLine("Wrong input! Enter choice number again:");
}
static void Main(string[] args)
{
Console.WriteLine("Please enter a number from 1 to 10");
int counter = Convert.ToInt32(Console.ReadLine());
//Here is your variable
Console.WriteLine("The numbers start from");
do
{
counter++;
Console.Write(counter + ", ");
} while (counter < 100);
Console.ReadKey();
}
You could create your own ReadInt function, that only allows numbers
(this function is probably not the best way to go about this, but does the job)
public static int ReadInt()
{
string allowedChars = "0123456789";
ConsoleKeyInfo read = new ConsoleKeyInfo();
List<char> outInt = new List<char>();
while(!(read.Key == ConsoleKey.Enter && outInt.Count > 0))
{
read = Console.ReadKey(true);
if (allowedChars.Contains(read.KeyChar.ToString()))
{
outInt.Add(read.KeyChar);
Console.Write(read.KeyChar.ToString());
}
if(read.Key == ConsoleKey.Backspace)
{
if(outInt.Count > 0)
{
outInt.RemoveAt(outInt.Count - 1);
Console.CursorLeft--;
Console.Write(" ");
Console.CursorLeft--;
}
}
}
Console.SetCursorPosition(0, Console.CursorTop + 1);
return int.Parse(new string(outInt.ToArray()));
}
Declare a variable that will contain the value of the user input :
Ex :
int userInput = Convert.ToInt32(Console.ReadLine());
I know this question is old, but with some newer C# features like lambda expressions, here's what I actually implemented for my project today:
private static async Task Main()
{
// -- More of my code here
Console.WriteLine("1. Add account.");
Console.WriteLine("2. View accounts.");
int choice = ReadInt("Please enter your choice: ");
// -- Code that uses the choice variable
}
// I have this as a public function in a utility class,
// but you could use it directly in Program.cs
private static int ReadInt(string prompt)
{
string? text;
do
{
Console.Write(prompt);
text = Console.ReadLine();
} while (text == null || !text.Where(c => char.IsNumber(c)).Any());
return int.Parse(new string(text.Where(c => char.IsNumber(c)).ToArray()));
}
The difference here is that if you accidentally type a number and any other text along with that number, only the number is parsed.
You could just go ahead and try :
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice=int.Parse(Console.ReadLine());
That should work for the case statement.
It works with the switch statement and doesn't throw an exception.
C# HOMEWORK QUESTION: I am creating a console application that prompts for two integers, prompts for which math operation to perform, and returns the results. I was able to get it to work with my two operands hardcoded, and now I'm trying to instantiate two separate objects through user input instead of a hardcoded variable. I've stripped it down to the barebones code that I'm having issues with, and I suspect the problem has something to do with the way I'm creating two objects from the same method...but I'm not sure what.
Here's my main class...
public class MainModule
{
public static void Main(string[] args)
{
// get Operands
Console.WriteLine("You Will Be Entering Two Integers.\n");
//
MathUI myOperand1 = new MathUI();
int op1 = myOperand1.EnterInteger();
//
MathUI myOperand2 = new MathUI();
int op2 = myOperand2.EnterInteger();
Console.WriteLine("You chose {0} and {1}.", (int)op1, (int)op2);
Console.ReadLine();
}
}
...and the MathUI class that accepts inputs.
public class MathUI
{
public int EnterInteger()
{
Console.Write("Enter an integer: ");
int enteredInteger = Console.Read();
return (enteredInteger);
}
}
When I execute the program, I get a prompt for an integer. I enter, for instance, 3, here's my output.
You Will Be Entering Two Integers.
Enter an integer: 3
Enter an integer: You chose 51 and 13.
Math demo completed
Press <enter> to quit
When I press enter after entering the first integer, I automatically get a second integer; and when I try to output the integer values, they don't match my input.
What's going on here? Is there something wrong with the way that I'm instantiating MathUI and my two operands? Do I only need to instantiate one instance of MathUI then declare both variables under that one instance? I'm also not sure why the integer output does not match my input. All the variables are cast as int, so I should have int all the way through, right? I tried casting these as integers--(int)op1--just in case op1 was held in some internal form...but don't know what's going on there.
What am I missing?
you need to make the Console.Read a Console.ReadLine as readline is triggered by the return key.
public class MathUI
{
public int EnterInteger()
{
Console.Write("Enter an integer: ");
int enteredInteger = Convert.ToInt32(Console.ReadLine());
return (enteredInteger);
}
}
Problem is that you are using Console.Read method which returns a value after any key has been pressed. Also, result it returns is ASCII value of key pressed. In your case, you pressed 3 which has ordinal (ASCII) value of 51 in decimal system and then ENTER which has value 13. If you look at MSDN documentation, Console.Read returns an integer.
To read value user entered as a string, use Console.ReadLine method.
If you really need to read in key by key, you can use Convert.ToChar, and then ToString method to get entered key as string. Like so:
string key = Convert.ToChar(Console.ReadLine()).ToString();
Or you can use following code to read actual operand
int intOperand;
if (!int.TryParse(Console.ReadLine(), out intOperant))
Console.WriteLine("You pressed non-numeric key");
Use Console.ReadLine instead of Console.Read. With Console.Read, the return character is being passed as input to the second Read call.
Also note that the int that is returned by Console.Read is not parsing a numeric number, it is giving you the Unicode character value of the entered char. This is why you are getting the "wrong" numbers.
You need to use Console.ReadLine and parse the string result like so:
public class MathUI
{
public int EnterInteger()
{
Console.Write("Enter an integer: ");
int enteredInteger = int.Parse(Console.ReadLine());
return (enteredInteger);
}
}
A couple other notes for your consideration:
There's no need to cast the values in the Console.WriteLine call.
You can make the MathUI class and EnterInteger method static.