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I cooked this up and was wondering if there is a better way to do this.
```Console.WriteLine("Name me.");
String cn = Console.ReadLine();
Console.WriteLine($"I like this name ,{cn}, What is my funcion? ");
String fn = Console.ReadLine();
Console.WriteLine($"I will learn how to do {fn} for you.");
Console.WriteLine("I Will double any number you give me.");
int a = Convert.ToInt32(Console.ReadLine());
int b = 2;
Console.WriteLine(a * b);
```
"Best" is subjective, but there are a few problems with the code:
Any non-number string entered will throw an exception
Any decimal number string will also throw an exception.
Instead of using Convert.ToInt32, you should consider using the TryParse method instead. This method takes in a string and an out parameter that gets set to the converted value if it's successful (otherwise 0), and it returns a bool that indicates success. If we use the decimal type, we will end up with a number that has very good precision and can include decimals.
If we then create a method with a loop that uses the result of TryParse as a condition, we can loop until the user enters a correct number.
We could also allow the user to pass in a validation method, so that they can specify what the rules are for a "valid" number (i.e. if it must be greater than zero, or must be odd, etc.).
Then we might end up with something like this:
public static decimal GetDecimalFromUser(string prompt,
Func<decimal, bool> validator = null)
{
bool isValid = true;
decimal result;
do
{
if (!isValid)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Invalid input, please try again.");
Console.ResetColor();
}
else isValid = false;
Console.Write(prompt);
} while (!decimal.TryParse(Console.ReadLine(), out result) &&
(validator == null || !validator.Invoke(result)));
return result;
}
Similarly, we can write code that prompts the user for string input. This will save us a few lines of code in our Main method, because we don't have to keep writing Console.WriteLine and Console.ReadLine:
public static string GetStringFromUser(string prompt)
{
Console.Write(prompt);
return Console.ReadLine();
}
Now we can write code where the user cannot enter invalid input! In use, the code would then look like:
string name = GetStringFromUser("Please give me a name: ");
string fn = GetStringFromUser($"I like this name, {name}. What is my function? ");
Console.WriteLine($"I will learn how to do {fn} for you.");
decimal input = GetDecimalFromUser("Please enter a number and I will double it: ");
Console.WriteLine($"{input} * 2 = {input * 2}");
Related
This question already has answers here:
How to validate user input for whether it's an integer?
(10 answers)
Closed 4 years ago.
So i nearly have 2k lines of code and i have forgotten to / i do not know how to have input valdation on user inputs such as
cw("Hello Please Enter your age");
cw("If you are in a Group Input the Age of the Youngest Member of the Group.");
Age = Convert.ToInt32(Console.ReadLine());
I want to Make it so that users can enter only numbers and my program will not crash when they put in somthing els.
this is a common problem in the whole of my program for the console.readlines.
Is there a way on mass that i can introduce the input valdation for numbers only and letters only when approate?
thank you in advance.
This is what I'd do (after a little more polish):
public static bool PromptForInt(string promptString, out int result, string helpString = null)
{
while (true)
{
Console.WriteLine(promptString);
var response = Console.ReadLine();
if (string.Equals(response, "Q", StringComparison.OrdinalIgnoreCase))
{
result = 0;
return false;
}
if (helpString != null && string.Equals(response, "H", StringComparison.InvariantCultureIgnoreCase))
{
Console.WriteLine(helpString);
continue; //skip back to the top of the loop
}
if (int.TryParse(response, out result))
{
return true;
}
}
}
You could right similar functions for other types (for example, double or DateTime, always using typeName.TryParse.
In terms of polishing, you might want to have a useful error message if the user doesn't enter "Q", "H" or a valid int. Otherwise...
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Below is the code for addition of two numbers. I ask for user input and validate the same in the function - GetValidateInput(). Code is working fine, but is it correct approach to ask for user input from user-defined function or we should do this in Main() and only validate the data in user-defined function (so that this function can be reused for other validation in some other places). What is the right approach?
class Solution
{
static void Main(string[] args)
{
Console.WriteLine("Enter the First Number");
int firstNumber = GetValidateInput();
Console.WriteLine("Enter the Second Number");
int secondNumber = GetValidateInput();
int sum = SolveMeFirst(firstNumber, secondNumber);
Console.WriteLine("The Sum is {0}",sum);
Console.ReadLine();
}
static int SolveMeFirst(int firstNumber, int secondNumber)
{
return firstNumber + secondNumber;
}
static int GetValidateInput()
{
bool isValid = false;
string number = null;
int result;
do
{
number = Console.ReadLine();
if (int.TryParse(number, out result))
isValid = true;
else
Console.WriteLine("Invalid Number, please re-enter");
} while (!isValid);
return result;
}
}
I typically try to keep the UI code separate from the business logic code, which means that, for the most part, I don't have calls to Console.ReadLine or Console.WriteLine in most methods.
Having a helper library that does input validation, however, is essential if you're doing a lot of user interaction through a Console. I have a library with methods similar to yours, only which take in the prompt to display to the user as an argument, so the method can be reused. The simplest version might look something like this:
public static int GetIntFromUser(string prompt)
{
int input;
do
{
Console.Write(prompt);
} while (!int.TryParse(Console.ReadLine(), out input));
return input;
}
Then you can call it like this:
int firstNumber = GetIntFromUser("Enter the First Number");
int secondNumber = GetIntFromUser("Enter the Second Number");
I have similar methods for different types, so I don't have to worry about data validation in my main code.
This question already has answers here:
C# How to loop user input until the datatype of the input is correct?
(4 answers)
Closed 6 years ago.
I trying to solve this code so it repeats exception until input is a number. right now it stop right first attempt and I do know how to place while loop.
int nomer2;
WriteLine("Write Number");
try
{
nomer2 = Convert.ToInt32(ReadLine());
WriteLine("here is my Number {0}", nomer2);
}
catch (Exception)
{
WriteLine("Error: Enter Number");
}
Its recommended not to use exceptions unless it is really unexpected what the result would be. You can use the TryParse function which tries to convert the string that is passed to it to an integer. If the conversion was successful, the integer is returned by reference in the second param and the function returns true, otherwise, it returns false.
int nomer2;
string input = string.Empty;
do
{
Console.WriteLine("Write Number");
input = Console.ReadLine();
}
while (!int.TryParse(input, out nomer2)) ;
Console.WriteLine("here is my Number {0}", nomer2);
while(!int.TryParse(ReadLine(), out nomer2))
{
WriteLine("Write Number");
}
WriteLine("here is my Number {0}", nomer2);
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Console.WriteLine("Enter value for Monday : ");
milesMon = Console.ReadLine();
try
{
dblMon = double.Parse(milesMon);
}
catch
{
Console.WriteLine("You entered an invalid number - a default of 0 has been set");
dblMon = 0;
while (true) break;
Console.WriteLine("Enter value for Monday : ");
milesMon = Console.ReadLine();
In it's current state the code only prompts the user after they enter incorrect data the first time they do it, I would like to know how to make it so it happens every time.
-Thanks
You should use a do or while loop to keep repeating the prompt until a valid double is entered. You should also consider adding some form of exit keywords. Like if they enter "exit, quit, q" etc.. Have it terminate the app instead of loop back around. However being a console app, ctrl + c will close it regardless of what it's doing (it's the kill command) but not everyone knows that.
bool repeat = true;
var dblMilesMon = (double)0;
do
{
Console.WriteLine("Enter value for Monday : ");
var strMilesMon = Console.ReadLine();
if (!double.TryParse(strMilesMon, out dblMilesMon))
Console.WriteLine("You entered an invalid number - please enter a numeric value.")
else
repeat = false;
}while (repeat);
//do something with dblMilesMon
You can use TryParse() to convert the input string to double, it will return false if the conversion failed; based on that input you can prompt the user that whether the input is valid or not. and this will loop until the user enter Exit
string inputVal = "";
double inputDoubleVal;
while (inputVal == "Exit")
{
Console.WriteLine("Enter value for Monday : ");
inputVal = Console.ReadLine();
if (double.TryParse(inputVal, out inputDoubleVal))
{
//Process with your double value
}
else
{
Console.WriteLine("You entered an invalid number - a default of 0 has been set");
}
}
Basically you want to write a loop. While the input is invalid, prompt the user. So you should have a bool variable called valid to indicate whether the input is valid. And than a while loop like this:
while (!valid) {
//...
}
In the while loop, prompt the user. So the code looks like this:
bool valid = false;
int input = 0;
while (!valid) {
Console.WriteLine ("Prompt");
try
{
input = Convert.ToInt32 (Console.ReadLine ());
valid = true;
}
catch {}
}
Hope this helps!
You can use recursion to create your end-less loop without using a for or while.
Also, instead of a try-catch statement, better use a TryParse
Doc ref: https://msdn.microsoft.com/en-us/library/bb384043.aspx
public int readInput(){
int val = 0;
Console.WriteLine("Enter a valid int");
string enteredVal = Console.ReadLine();
bool result = int.TryParse(enteredVal, out val);
if(result)
return val;
Console.writeLine("Try again, only int values allowed");
return readInput();
}
int val = readInput();
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I am having this really annoying issue (I know this is basic stuff) but when I try use tryparse, I have to enter 2 values before it says integer, I want it to say integer after 1 try. (btw I have to use tryparse)
here is an example.
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
int results = 0;
Console.WriteLine("how old are you?");
int.TryParse (Console.ReadLine(), out results);
if (int.TryParse (Console.ReadLine(), out results))
{
Console.WriteLine("integer");
}
else
{
Console.WriteLine("not an integer");
}
Console.ReadLine();
}
}
}
Use variables for Console.ReadLine() and int.TryParse:
Console.WriteLine("how old are you?");
string input = Console.ReadLine().Trim();
bool success = int.TryParse(input, out results);
if ( success )
{
Console.WriteLine("{0} is an integer", input); // results has the correct value
}
else
{
Console.WriteLine("{0} is not an integer", input);
}
Get rid of the first redundant call to TryParse e.g.
class Program
{
static void Main(string[] args)
{
int results = 0;
Console.WriteLine("how old are you?");
//int.TryParse(Console.ReadLine(), out results); <-- remove this
if (int.TryParse (Console.ReadLine(), out results))
{
Console.WriteLine("integer");
}
else
{
Console.WriteLine("not an integer");
}
Console.ReadLine();
}
}
Int32.TryParse converts the string representation of a number to its 32-bit signed integer equivalent.
A return value indicates whether the conversion succeeded.
So you can always use it like this.
if (int.TryParse (Console.ReadLine(), out results))
{
Console.WriteLine("integer");
}
On top of the other answers you may wish to do the TryParse in a while loop so that users must enter a valid integer
while(!int.TryParse(ConsoleReadLine(), out results)
Console.WriteLine("not an integer");
ConsoleWriteLine("integer");
To better explain your current issue, you are asking the user to enter two integers, but you only ever care about the second one. The first one is assigned to results but then it is overriden the next time you call TryParse without ever being used