I'm pretty new to C# and am wondering how I'd go about validating user input to meet the following requirements:
has to be a decimal type. if it isn't it should ask the user to enter a decimal value. (Which i believe i have covered in my code below)
also has to be within a specific range (1 - 1,000,000). If it isn't it should ask the user to enter a number within the correct range
What's the most efficient way of doing this considering i will have multiple user input to validate in the same sort of way.
decimal balance;
Console.Write("Starting Balance: $");
while (!decimal.TryParse(Console.ReadLine(), out balance))
{
Console.Write("Please enter a valid decimal value: $");
}
EDITED BELOW
How about this?
decimal balance;
Console.Write("Starting Balance: $");
while(true)
{
if (!decimal.TryParse(Console.ReadLine(), out balance))
Console.Write("Please enter a valid decimal value: $");
else if (balance < 1 || balance > 100)
Console.Write("Please enter an amount between 1 and 100: ");
else
break;
}
Console.WriteLine("Balance entered is: " + balance.ToString("n"));
return val; line gave me an error so i left it out but the above seems to work?
I'd try something like:
decimal GetUserInput(string inputQuery, decimal min, decimal max)
{
Console.Write(inputQuery);
decimal val;
while(true)
{
if(!decimal.TryParse(Console.ReadLine(), out val))
Console.Write("Please enter a valid decimal value: $");
else if(val < min || val > max)
Console.Write("Please enter an amount between " + min + " and " + max + ": $");
else // the value is a decimal AND it's correct
break;
}
return val;
}
Then use it like:
var startingBalance = GetUserInput("Starting Balance: $", 1, 100000);
var endingBalance = GetUserInput("Ending Balance: $", 1, 100000);
//...
If your min and max are fixed, then you could not pass them as arguments and use a fixed check. And you could also avoid having the query : $ passed in if needed, but I'll leave that to you
Update
The reason why the return val line was giving you an error was because you were inlining it (probably in a void returning function). What I was doing was making a function since you specified it needed to be reusable.
So in your program, you need to make a separate function... your program would look something like this:
class Program
{
// We're declaring this function static so you can use it without an instance of the class
// This is a function, so it can be called multiple times, with different arguments
static decimal GetUserInput(string inputQuery, decimal min, decimal max)
{
// Write the argument "inputQuery" to console
Console.Write(inputQuery);
decimal val;
// Loop indefinitely
while(true)
{
// Read from console into a decimal "val"
if(!decimal.TryParse(Console.ReadLine(), out val))
// It was not a correct decimal, so write the prompt
Console.Write("Please enter a valid decimal value: $");
// It was a correct decimal
else if(val < min || val > max)
// But not in range, so write a different prompt
Console.Write("Please enter an amount between " + min + " and " + max + ": $");
// It was a decimal and within range
else
// so we break the infinite loop and exit after the "}"
break;
// If we have got to this point (we didn't hit the "break"),
// it was either not a decimal or it wasn't within range,
// so it'll loop again and ask for a value from console again.
// The prompt was already written above (in the "ifs")
}
// We got out of the while(true){} loop, so it means we hit "break"
// above, and that means "val" contains a correct value (decimal and
// within range), so we return it to the caller
return val;
}
static void Main()
{
// Your original code went here, but see how my function is *outside* function Main()
// You use my function (GetUserInput) here:
var startingBalance = GetUserInput("Starting Balance: $", 1, 100000);
var endingBalance = GetUserInput("Ending Balance: $", 1, 100000);
// Then with the returned values (stored in "startingBalance"
// and "endBalance"), you can do what you want:
Console.WriteLine("Starting balance was: " + startingBalance.ToString("n"));
}
}
I've made a fiddle with the whole program so you can test online and make changes: https://dotnetfiddle.net/HiwwIP
If I were you, I would do such:
bool isInvalid, isOutOfRange;
decimal balance = 0;
isOutOfRange = true;
do
{
string input = Console.ReadLine();
isInvalid = !Decimal.TryParse(input, out balance);
if (!isInvalid)
{
// use balance<=1 if 1 should not be included
// use balance>=1000000 if 1000000 should not be included
isOutOfRange = (balance < 1 || balance > 1000000);
}
if (isInvalid)
{
Console.WriteLine("Please enter a valid decimal value: $");
}
else if (isOutOfRange)
{
Console.WriteLine("Please enter value between 1 and 1000000: $");
}
} while (isInvalid || isOutOfRange);
Console.WriteLine("{0}, That is a valid value!", balance.ToString());
Console.ReadKey();
Of course you can shortcut by eliminating bool definitions and directly calling functions instead; but I wrote in detail for clarity as you indicated that you are "pretty new".
Related
I want to the result print out like this:
this is your stamp duty: result.
However, i just get the number only, am i wrong some where?
using System;
namespace simple_application
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("This is the test for calculate the stamp duty");
Console.Write("Please enter your value of the vehicle: ");//so i let the input here
decimal vehicle_value = Convert.ToDecimal(Console.ReadLine());
if (vehicle_value <= 45000)
{
Console.WriteLine(vehicle_value / 100 * 3);
decimal number1 = Convert.ToDecimal(Console.ReadLine());
Console.WriteLine(number1);
Console.WriteLine("this is your stamp duty: "+ number1); // message + output
}
else//if the money greater than 45000
{
Console.WriteLine((vehicle_value - 45000) / 100 * 5 + 1350);
decimal number2 = Convert.ToDecimal(Console.ReadLine());
Console.WriteLine("This is your stamp duty: " + number2); // message + output
}
}
}
}
So the thing is I have tried so many different types of ways to contain a value like int, float, or long but it just not work?
I think you are calling Console.ReadLine() too many times, just calculate the values that you need and output them:
using System;
namespace simple_application
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("This is the test for calculate the stamp duty");
decimal vehicle_value;
do
{
Console.Write("Please enter your value of the vehicle: "); //so i let the input here
}
while (!decimal.TryParse(Console.ReadLine(), out vehicle_value));
if (vehicle_value <= 45000)
{
decimal number1 = vehicle_value / 100 * 3;
Console.WriteLine("this is your stamp duty: " + number1); //message+output
}
else //if the money greater than 45000
{
decimal number2 = (vehicle_value - 45000) / 100 * 5 + 1350;
Console.WriteLine("This is your stamp duty: " + number2); //message+output
}
}
}
}
Also I've replaced Convert.ToDecimal by a loop calling Decimal.TryParse, so it doesn't fail on invalid input.
Remove this line and the code should work as expected
Console.WriteLine(number1);
using System;
namespace test
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("This is the test for calculate the stamp duty");
Console.Write("Please enter your value of the vehicle: ");//so i let the input here
decimal vehicle_value = Convert.ToDecimal(Console.ReadLine());
if (vehicle_value <= 45000)
{
decimal num1 = vehicle_value / 100 * 3;
Console.WriteLine("this is your stamp duty: {0}", num1); // message + output
}
else//if the money greater than 45000
{
decimal num2 = (vehicle_value - 45000) / 100 * 5 + 1350;
Console.WriteLine("This is your stamp duty: {0}", num2); // message + output
}
}
}
}
What I have here is a small console app I'm wanting the user to type in their monthly salary then their "Expenses" To calculate how much money they have over the month once they take away their expenses (A calculator that tells the user how much money they have monthly once all bills are paid). I'd like to take away from int Salary. I want the expenses to keep populating until the user types "false", in the bool FinishedAdding currently the variable Expenses only holds one value, I want to add all Expenses then subtract from Salary. Am I doing this correctly or is this the wrong approach?
string NewLine = "\n";
bool Finished = false;
var Expenses = default(int);
Console.WriteLine("Enter you earn a month (after tax");
int Salary = Convert.ToInt32(Console.ReadLine());
Console.WriteLine(NewLine);
if (Finished != true)
{
while (Finished == false)
{
Console.WriteLine("What are your expenses");
Expenses = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("You are finished?");
bool FinishedAdding = Convert.ToBoolean(Console.ReadLine());
if (FinishedAdding == true)
{
break;
}
}
}
Console.WriteLine(NewLine);
Console.WriteLine("Your total is: " + (Expenses - Salary));
Couple changes I made:
1) Most importantly: Expenses += will add what they enter each time to the amount they entered previously. This will be your total expenses that you can then subtract from Salary.
2) Instead of using a separate variable for Finished, just set the Finished variable to whether or not they enter "true" or "false".
3) No need for an if and break statement, just let the while criteria check the Finished variable.
string NewLine = "\n";
bool Finished = false;
var Expenses = default(int);
Console.WriteLine("Enter you earn a month (after tax)");
int Salary = Convert.ToInt32(Console.ReadLine());
Console.WriteLine(NewLine);
while (Finished == false)
{
Console.WriteLine("What are your expenses");
Expenses += Convert.ToInt32(Console.ReadLine());
Console.WriteLine("You are finished?");
Finished = Convert.ToBoolean(Console.ReadLine());
}
Console.WriteLine(NewLine);
Console.WriteLine($"Your total is: {(Salary - Expenses)}");
Let's implement the routine step by step. We can start from reading decimal (which better fits financial data like Salary)
// Either enter valid decimal value or press enter (for exit)
private static bool TryReadDecimalOrExit(string title, out decimal value) {
value = 0m;
while (true) {
if (!string.IsNullOrWhiteSpace(title))
Console.WriteLine(title);
string input = Console.ReadLine();
if (string.IsNullOrWhiteSpace(input))
return false;
if (decimal.TryParse(input, out value))
return true;
Console.WriteLine("Sorry, invalid value. Please, try again");
}
}
private static decimal ReadDecimal(string title) {
while (true) {
if (!string.IsNullOrWhiteSpace(title))
Console.WriteLine(title);
string input = Console.ReadLine();
if (decimal.TryParse(input, out value))
return value;
Console.WriteLine("Sorry, invalid value. Please, try again");
}
}
Time to loop:
decimal Salary = ReadDecimal("Enter you earn a month (after tax");
Decimal Expenses = 0m;
// While not exited, ask for a new expense
while (TryReadDecimalOrExit("What are your expenses", out var expense))
Expenses += expense;
Console.WriteLine("Your total is: {Salary - Expenses:c2}");
With
Expenses = Convert.ToInt32(Console.ReadLine());
you are assigning a value to Expenses with each iteration. Since the expenses of the user do not equal the last amount they spent, but the summed amount, you'd have to sum up the expenses
Expenses = Expenses + Convert.ToInt32(Console.ReadLine());
This can be simplified with +=, which is basically "add a value to the contents of a variable and assign the new value to the variable". This yields
Expenses += Convert.ToInt32(Console.ReadLine());
On a side note
There is no error handling. Your program will crash if I enter e.g. ei19 as the amount. While the answer of Dmitry provides an approach to error handling in your program, it will exit as soon as you type something that is not a number. You might want to check whether the input is valid ans display an error message
while(!Finish)
{
var input = ReadInput("Your message");
if(ShouldExit(input))
{
Finish = true;
}
else if(IsValidAmount(input))
{
Expenses = input.Amount;
}
else
{
WriteErrorMessage("Your error message");
}
}
if input being of type UserInput for example
class UserInput
{
// ...
public bool Finished { get; }
public Decimal Amount { get; }
}
just for the gist of it.
string NewLine = "\n";
bool Finished = false;
var Expenses = default(int);
Console.WriteLine("Enter you earn a month (after tax");
int Salary = Convert.ToInt32(Console.ReadLine());
Console.WriteLine(NewLine);
while (!Finished)
{
Console.WriteLine("What are your expenses");
Expenses += Convert.ToInt32(Console.ReadLine());
Console.WriteLine("You are finished?");
Finished = Convert.ToBoolean(Console.ReadLine());
}
Console.WriteLine(NewLine);
Console.WriteLine("Your total is: " + (Salary - Expenses));
Basically I'm trying to not let the user input string instead of an integer; but on line of code:
else if (Convert.ToString(result) == "")
I get an error.
Full code:
class Program
{
static void Main(string[] args)
{
Console.ForegroundColor = ConsoleColor.Red;
int calcKelvin = 273;
int calcFahren = 32;
int result = Convert.ToInt32(Console.ReadLine());
if (result == 0)
{
Console.WriteLine("Check it up on google!");
Console.Title = "I'M USELESS CONSOLE, YOU CAN NOW EXIT || I'M USELESS CONSOLE, YOU CAN NOW EXIT || I'M USELESS CONSOLE, YOU CAN NOW EXIT ||";
}
else if (Convert.ToString(result) == "")
{
Console.Write("Error, you can not convert a text");
}
else
{
Console.WriteLine("Kelvin = " + calcKelvin * result);
Console.WriteLine("Fahrenheit = " + calcFahren * result);
}
}
}
The safest way to get a number from a string is to use the TryParse method, because this method returns two values! The actual return type is a bool which indicates whether or not the string was successfully converted, and the other is an out parameter, which is of the type that we're converting to, and which gets set to the converted value (or is set to the default value of the type if the conversion fails).
For temperatures, we often deal with decimal numbers, so a double is probably a good type to store the result. So, we'll use double.TryParse.
Now, since we don't necessarily want to just quit if the user makes a mistake, we should probably do our conversion in a loop, so if it fails, we just ask the user to try again. And since this code will be used in other places as well, we can make a helper method that takes in a prompt that we display to the user, and returns the strongly-typed user response:
private static double GetDoubleFromUser(string prompt = null)
{
double result;
do
{
Console.Write(prompt);
} while (!double.TryParse(Console.ReadLine(), out result));
return result;
}
With this method, we can now just declare a double and assign it to the return value of the method above, like:
double userInput = GetDoubleFromUser("Enter a temperature: ");
Another thing we can correct in the code are the formulas used to do the conversions. A quick check online shows us that we add a number for kelvin and we do multiplication, division, and addition for Fahrenheit. We can calculate these values on the fly once we have the Celsius temperature from the user:
private static void Main()
{
double celcius = GetDoubleFromUser("Enter a Celcius temperature: ");
double fahrenheit = celcius * 9 / 5 + 32;
double kelvin = celcius + 273.15;
Console.WriteLine("Kelvin = " + kelvin);
Console.WriteLine("Fahrenheit = " + fahrenheit);
GetKeyFromUser("Done! Press any key to exit...");
}
Output
Convert.ToInt32 throws an exception if the input string is not a number. To fix that, you can use int.TryParse instead.
Example:
using System;
class Program
{
static void Main(string[] args)
{
Console.ForegroundColor = ConsoleColor.Red;
int calcKelvin = 273;
int calcFahren = 32;
int result;
bool isNum=int.TryParse(Console.ReadLine(),out result);
if (!isNum)
{
Console.Write("Error, you can not convert a text");
}
else if (result == 0)
{
Console.WriteLine("Check it up on google!");
Console.Title = "I'M USELESS CONSOLE, YOU CAN NOW EXIT || I'M USELESS CONSOLE, YOU CAN NOW EXIT || I'M USELESS CONSOLE, YOU CAN NOW EXIT ||";
}
else {
Console.WriteLine("Kelvin = " + calcKelvin * result);
Console.WriteLine("Fahrenheit = " + calcFahren * result);
}
}
}
The subject is a little problem:
Write a program and continuously ask the user to enter a number or "ok" to exit. Calculate the sum of all the previously entered numbers and display it on the console.
Here is my code:
var sum = 0;
while (true)
{
Console.WriteLine("Enter a number or ok to exit:");
if (Console.ReadLine() == "ok") break;
sum += Convert.ToInt32(Console.ReadLine());
Console.WriteLine(sum);
}
When I tap ok, it terminate.
When I tap number and enter, it shows system.formatexception:The input string is not in the correct format.
I know one of the solution is
var sum = 0;
while (true)
{
Console.Write("Enter a number (or 'ok' to exit): ");
var input = Console.ReadLine();
if (input.ToLower() == "ok")
break;
sum += Convert.ToInt32(input);
}
Console.WriteLine("Sum of all numbers is: " + sum);
Maybe My code looks a little weired, But Why is my code wrong?
Reason is input will be "ok". Can not convert that into an integer.
first you have to store the first input value into other variable.
then convert that string into integer and get summation.
var sum = 0;
while (true)
{
Console.Write("Enter a number (or 'ok' to exit): ");
var input = Console.ReadLine();
int newVariable = 0;
if (input.ToLower() != "ok")
{
newVariable = Convert.ToInt32(input);
}
input = Console.ReadLine();
if (input.ToLower() == "ok"){
break;
sum += newVariable;
}
}
Console.WriteLine("Sum of all numbers is: " + sum);
If there any problem here please let me know.
Try this:
var sum = 0;
while (true)
{
Console.WriteLine("Enter a number or ok to exit:");
String ans = Console.ReadLine();
if (ans == "ok" || ans.ToLower() == "ok") break;
sum += Convert.ToInt32(ans);
Console.WriteLine(sum);
}
Here I've just store input entered by user in one variable and use that variable in further process.
In your first code you have take input two times, first one is in IF condition and second in parsing, that may cause the problem.
The correct way to do this is to use int.TryParse for your conversion from a string to a number. TryParse attempts to convert the string to a number, but if it cannot do so (for example, the string contains more than just numeric digits) it will fail gracefully instead of causing an exception. The other answers so far will all cause an unhandled FormatException if something non-numeric is entered other than "ok". By using int.TryParse you can handle the case where it's a valid number, as well as the case where it is invalid, and then alert the user. Here's an example within the context of your code:
// I prefer using concrete types for numbers like this, so if anyone else
// reads it they know the exact type and numeric limits of that type.
int sum = 0;
int enteredNumber = 0;
while (true)
{
Console.Write("Enter a number (or 'ok' to exit): ");
var consoleInput = Console.ReadLine();
if (consoleInput.ToLower() == "ok")
break;
if(int.TryParse(consoleInput, out enteredNumber))
{
sum += enteredNumber;
}
else
{
Console.WriteLine("You entered '" + consoleInput + "', which is not a number.");
}
}
Console.WriteLine("Sum of all numbers is: " + sum.ToString());
This is better because you know you have no control over the user's input other than to validate it yourself, and so it's better to speculatively convert the number and be alerted to success or failure without triggering an exception. Wrapping everything with a try/catch block is not a proper solution.
Your first code example, as rightly pointed out in the comments, reads a line, tests it for 'ok', then throws it away, reads another line, and uses that to add to the sum, which is not what you wanted.
After some quick research, I would say the most concise way to handle this in C# is probably something like your second code example. In F# I was able to come up with the following examples (one is a loop, the other uses sequences, i.e. IEnumerable<_>s) but I found no concise way to get the same with C# and LINQ…
let inputLoop () =
let rec aux sum =
match stdin.ReadLine () with
| "ok" -> sum
| s -> aux (sum + int s)
stdout.WriteLine (aux 0 |> string)
let inputSeq () =
fun _ -> stdin.ReadLine ()
|> Seq.initInfinite
|> Seq.takeWhile (fun s -> s <> "ok")
|> Seq.sumBy int
|> string
|> stdout.WriteLine
Try it :)
var sum = 0;
while (true)
{
Console.Write("Enter a number: or ok to exit : ");
String input = Console.ReadLine();
if (input == "ok" || input.ToLower() == "ok") break;
if(string.IsNullOrWhiteSpace(input))
continue;
sum += Convert.ToInt32(input);
}
Console.WriteLine("Total Result: " + sum);
Write a program and continuously ask the user to enter a number or "ok" to exit. Calculate the sum of all the previously entered numbers and display it on the console. Happy Coding
var sum = 0;
while (true)
{
Console.Write("Write number or write \"ok\" for exit: ");
var input = Console.ReadLine();
if (input.ToLower() != "ok")
{
sum += Convert.ToInt32(input);
continue;
}
break;
}
Console.WriteLine("All sum: " + sum + ".");
This is one way to do it. I'm just learning to do this!
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Enter number to know the sum or press ok to exit and display the sum");
int sum = 0;
while (true) // to run the program continously asking user input
{
Console.WriteLine("Enter Number: ");
var input = Console.ReadLine(); // takes user input
if (input.ToLower() == "ok") // compares user input to string ok
break; //if user input is ok, breaks the loop and sum is displayed
var inputInInt = Convert.ToInt32(input); // if user input is int, continues to convert it to integer
sum += inputInInt; // user input in interger is added to sum
}
Console.WriteLine("The sum of entered numbers is: " + sum);
Console.ReadLine();
}
}
In C# I am trying to have the user input a number. I then want to check that
They have entered a string that can be converted to a double and
They have entered a value greater than zero
The method I have initially created was
string inValue;
double outcome;
Console.WriteLine("Enter amount: ");
inValue = Console.ReadLine();
while (double.TryParse(inValue, out outcome) == false)
{
Console.WriteLine("Initial value must be of the type double");
Console.WriteLine("\nPlease enter the number again: ");
inValue = Console.ReadLine();
}
outcome = double.Parse(inValue);
while (outcome < 0)
{
Console.WriteLine("Initial value must be of at least a value of zero");
Console.WriteLine("\nPlease enter the number again: ");
inValue = Console.ReadLine();
outcome = double.Parse(inValue);
}
return outcome;
The problem was this was that if the user entered say "-10" and then "f" an exception would occur. This is because the program would move past the first check (that checks for the double) for the value of -10 but then when the "f" is entered it throws an exception when only given the second test.
I believe the solution is to create a while statement that writes the error statement when either the value cannot be converted to a double or the value is converted to a double and is below zero. What I don't know how to do is to have the value be converted to a double and then evaluated as being greater than zero all in the while statement.
You're on the right track - you need to have a single while loop that gets the input and then tries both validations. One way to do this is to create a boolean value that tracks whether or not the value is valid, and then use that as the condition for the loop:
double outcome = 0;
bool valid = false;
while (!valid)
{
Console.WriteLine("Enter amount: ");
string inValue = Console.ReadLine();
if (double.TryParse(inValue, out outcome) == false)
{
Console.WriteLine("Initial value must be of the type double");
Console.WriteLine("\nPlease enter the number again: ");
}
else if (outcome < 0)
{
Console.WriteLine("Initial value must be of at least a value of zero");
Console.WriteLine("\nPlease enter the number again: ");
}
else
{
valid = true;
}
}
return outcome;
It's also possible to put both conditions in the while statement, but this approach lets you provide a different message depending on which conditions failed.
you can or those two conditions in your first while loop
something like
while (!double.TryParse(inValue, out outcome) || outcome < 0)
{
...
}
some explanation: double.TryParse will modify the value of outcome if it is successful, so if it was able to parse then the ! TryParse will be evaluated to false, thus we get to the second part and evaluate outcome < 0.
I would go with a solution like this. Just noting that you don't have to double.Parse(Value) after you have done a double.TryParse(value, out outcome) the out parameter will populate that variable upon the TryParse being true.
You can copy and paste the below code into LinqPad and play with it. But this does what you need.
void Main()
{
var result = DoWork();
Console.WriteLine(result);
}
public double DoWork()
{
string inValue;
double outcome;
Console.WriteLine("Enter amount: ");
inValue = Console.ReadLine();
while (!double.TryParse(inValue, out outcome) || outcome <= 0)
{
Console.WriteLine("Initial value must be of the type double and greater than 0");
Console.WriteLine("\nPlease enter the number again: ");
inValue = Console.ReadLine();
}
return outcome;
}
after a little regrouping it is working code!
but i think you sometimes need to use if instead of while
string inValue = "";
double outcome = -1;
Console.WriteLine("Enter amount: ");
while (outcome < 0){
inValue = Console.ReadLine();
if (double.TryParse(inValue, out outcome) == false)
{
Console.WriteLine("Initial value must be of the type double");
Console.WriteLine("\nPlease enter the number again: ");
continue;
}
if (outcome>=0) {continue;}
Console.WriteLine("Initial value must be of at least a value of zero");
Console.WriteLine("\nPlease enter the number again: ");
}
return outcome;