I am following a c# course and trying to upgrade my user input method to check if the entered console input is an integer. I have written myself into a do while loop that I know doesn't work, but I am struggling a bit with coming up with a method that can both check for value and if the entered variable is an integer.
So what I tried here was to do-while until the user entered input is an Integer and between the min and max values. But I get stuck on result is only set to a value in the 'if' block, not the 'else' block. It won't compile unless result is set to something, unassigned variable. And I understand why, because there is a branch where I end up with a variable without value, and that won't pass in my while greater-less comparisson. You can only compare numbers, not nulls or strings.
Should I abandon the do-while loop for something more clever? Right now my 'hack' is to set result = 0 in the case that TryParse is false.
That is only useful as long as the user does not need to input 0, in which case the whole thing makes no sense any longer.
static int readInt(string prompt, int low, int high) // METHOD readInt
{
int result;
bool succes;
do
{
int temp;
string intString = readString(prompt);
succes = Int32.TryParse(intString, out temp);
if (succes)
{ Console.WriteLine("The string was a number within the limits, {0}.", intString);
result = int.Parse(intString);
}
else
{
Console.WriteLine("{0} is not a valid number between {1} and {2}", intString, low, high);
result = 0;
}
} while (!succes && (result < low) || (result > high));
return result;
}
It might be easier to just use a while (true) loop and return from inside the loop when you have a valid result. This is a structured construct known as a loop with one exit, so it's fine to use (if you're worried about structured programming).
For example:
static int readInt(string prompt, int low, int high) // METHOD readInt
{
while (true)
{
string intString = readString(prompt);
if (Int32.TryParse(intString, out var result) && (result >= low) && (result <= high))
{
Console.WriteLine("The string was a number within the limits, {0}.", intString);
return result;
}
else
{
Console.WriteLine("{0} is not a valid number between {1} and {2}", intString, low, high);
}
}
}
Note the use of a relatively recent C# feature, the ability to declare an out variable at the point of use using the var keyword - see the out var result inside the TryParse().
Or for a simpler pattern
int result;
string intString;
while (!int.TryParse(intString = Console.ReadLine(), out result) || result < low || result > high)
Console.WriteLine($"{intString} is not a valid number between {low} and {high}");
Console.WriteLine("The string was a number within the limits, {result}.");
return result;
you can change your " result = int.Parse(intString);" in the "if" with "return temp";
you already have the number from your TryParse, so you do not need to parse it again; returning inside the "if" also removes the need to assign a value to 'result' inside the "else" in fact, you don't need "result" at all)
static int readInt(string prompt, int low, int high) // METHOD readInt
{
bool succes;
do
{
string intString = readString(prompt);
succes = Int32.TryParse(intString, out int temp);
if (succes)
{ Console.WriteLine("The string was a number within the limits, {0}.", intString);
return temp;
}
else
{
Console.WriteLine("{0} is not a valid number between {1} and {2}", intString, low, high);
}
} while (!succes && (result < low) || (result > high));
}
You had a couple of bugs in the code. This works:
static int readInt(int low, int high)
{
int result;
bool success;
bool outOfLimits = false;
do
{
Console.Write("Enter a number: ");
string intString = Console.ReadLine();
success = Int32.TryParse(intString, out result);
if (!success)
{
Console.WriteLine("{0} is not a valid number.", intString, low, high);
continue;
}
outOfLimits = result < low || result > high;
if (outOfLimits)
Console.WriteLine("The string was NOT a number between {1} and {2}.", intString, low, high);
else
Console.WriteLine("The string was a number within the limits, {0}.", intString);
} while (!success || outOfLimits);
return result;
}
When code evolves like yours, it sometimes gets a bit unclear what it does as the complexity rises. Usually that's a sign that you should refactor it.
I would try to make the code clearer by moving all the checks for validity into a method by itself. Then you can do something like this.
static int readInt(string prompt, int low, int high) // METHOD readInt
{
bool valid = false;
int result = 0;
while (!valid)
{
var intString = readString(prompt);
valid = checkIfValid(intString, low, high, out result);
}
return result;
}
static bool checkIfValid(string s, int low, int high, out int result)
{
if (!Int32.TryParse(s, out result))
{
Console.WriteLine(s + " isn't an integer");
return false;
}
if (result < low)
{
Console.WriteLine("Number is too low");
return false;
}
if (result > high)
{
Console.WriteLine("Number is too high");
return false;
}
return true;
}
Try implementing the routine validating the conditions one after one (we have no need to make code too complex with !succes && (result < low) || (result > high) check):
If user input a valid integer (int.TryParse)?
If valid is it within the range?
If any validation fails keep asking user:
static int readInt(string prompt, int low, int high)
{
// Keep on looping until we return a valid result
while (true)
{
// Or
// Console.WriteLine(prompt);
// string input = Console.ReadLine();
string input = readString(prompt);
int result = 0; // initialization: let the compiler be happy
if (!int.TryParse(input, out result)) // Do we have an syntactically invalid input?
Console.WriteLine($"{input} is not a valid integer number");
else if (result < low || result > high) // If result is valid; is it out of range?
Console.WriteLine($"{input} is out of [{low}..{high}] range");
else // result is valid integer and within the ranges: time to return it
return result;
}
}
Related
So my code is to check if a given number is a 'happy number'. It squares each digit of the number, adds them and continues to do so until either the result of the addition is 1 (which means it is a happy number) or until it results in a 4 (which means it is not a happy number).
What's happening is that there are many numbers which cause an infinite loop (therefore meaning they are not a happy number) and I'm wondering how I would construct my code so that it will detect when there's an infinite loop occuring? I have some ideas but all flawed.
My code is as follows:
using System;
namespace Happy_numbers_problem
{
class Program
{
static int HappyNumbers(string Number)
{
string Output = Number;
while ((Convert.ToInt32(Output) != 1) && (Convert.ToInt32(Output) != 4))
{
string Result2 = "0";
for (int Index = 0; Index < Output.Length; Index++)
{
string Character = Output.Substring(Index, 1);
int Calc = Convert.ToInt32(Character);
int Result = Calc * Calc;
//Adding Result2 and Result, then turning it into a string.
Result2 = Convert.ToString(Convert.ToInt32(Result2) + Result);
if (Index == (Output.Length) - 1)
{
Output = Result2;
}
}
}
return Convert.ToInt32(Output);
}
static void Main(string[] args)
{
Console.WriteLine("Please enter a number");
string Number = Console.ReadLine();
int Output = HappyNumbers(Number);
if (Output == 1)
{
Console.WriteLine(Number + " is a happy number");
}
else if (Output == 4)
{
Console.WriteLine(Number + " is not a happy number");
}
else
{
Console.WriteLine(Number + " is not a happy number");
}
}
}
}
The problem resides in your while condition. If your output needs to be 1 or 4 to break out of the loop and deliver the output to latter be analysed, you have to use the operator or || instead of the operator and &&.
I got an assignment where I have a few user inputs. My goal is that the user is only allowed to enter an integer. The program works as I want it to, but this message is messing with me.
What is the problem there, and how do I fix it?
static int Check_input(string input)
{
bool is_valid = Int32.TryParse(input, out int number);
if (is_valid)
{
number = 1;
}
else
{
number = 0;
}
return (number);
}
In the first line of your method bool is_valid = Int32.TryParse(input, out int number); you create a new variable number and assign a value to it. But you never use this value, because you immediately assign either the value 1 or 0 to it. Actually, you can shorten your code
static int Check_input(string input)
{
bool is_valid = Int32.TryParse(input, out _);
if (is_valid)
{
return 1;
}
else
{
return 0;
}
}
Here, you discard the out parameter of TryParse and only investigate its return value to check which value your method should return.
But actually, you should return a bool value to see whether the user entered a valid number, which would make your method look like this:
static bool Check_input(string input)
{
return Int32.TryParse(input, out _);
}
This is even simpler and it is easier to work with a boolean variable then with an integer that might be 1 or 0. Compare this:
if(Check_input("test") == 1)
{
Console.WriteLine("good input");
}
else
{
Console.WriteLine("bad input");
}
with
if(Check_input("test"))
{
Console.WriteLine("good input");
}
else
{
Console.WriteLine("bad input");
}
You wouldn't need to asign number with out int number, because you are setting it to 0 or 1 later anyway.
To be more accurate your if, else is useless anyway. You are already setting the number to either 1 or 0 or you wouldn't be able to set it equal to a bool anyway.
Fixed Code:
static bool Check_input(string input) {
bool is_valid = Int32.TryParse(input, out _);
return (is_valid);
}
I need to evaluate same conditional expression multiple times in code.
What is the best way to store and reevaluate the conditional expressions in C#
eg. I want to remove the duplication of conditional expression given in while and if without using additional function call
while(!int.tryparse(num) || num <= 0 || num > 2000)
{
num = console.ReadLine();
if(!int.tryparse(num) || num <= 0 || num > 2000)
{
console.write("There is an error in the input value");
}
}
Not sure if this is exactly what you're looking for, but one handy way to get strongly-typed (and otherwise valid) input from the user is to write a method that takes in a string prompt (which asks the user for some input) and an optional Func<int, bool> argument that returns true if the int meets some criteria. We can also have an optional error message to display if the input is incorrect.
Here's a method that I've used in the past:
public static int GetIntFromUser(string prompt, Func<int, bool> validator = null,
string error = null)
{
int result;
bool invalidInput = false;
do
{
if (invalidInput && !string.IsNullOrEmpty(error))
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine(error);
Console.ResetColor();
}
Console.Write(prompt);
invalidInput = true;
} while (!int.TryParse(Console.ReadLine(), out result) ||
(validator != null && !validator.Invoke(result)));
return result;
}
In use, it makes life really simple, because you never have to write the validation code again. Note that we can just write an in-line lambda expression for our validator argument:
int input = GetIntFromUser("Enter a number from 0 to 2000: ",
x => x >= 0 && x < 2000, "Invalid number, try again.");
Output
Now, if we want to use the exact same validation over and over again (in different areas of code, outside of a loop), we can extract the above method call to a Func<int> and call it whenever we want:
Func<int> ZeroTo2000 = () => Temp.GetIntFromUser("Enter a number from 0 to 2000: ",
x => x >= 0 && x < 2000, "Invalid number, try again.");
int input1 = ZeroTo2000();
int input2 = ZeroTo2000();
Extract to a separate method.
public bool IsValid(string input)
{
if (!int.TryParse(input, out var result)) return false;
return (result > 0 && result <= 2000);
}
Then you can use it like this (your original code had problems which I fixed):
while (true)
{
num = Console.ReadLine();
if (IsValid(num)) break;
Console.WriteLine("There is an error in the input value");
}
You can combine both the code for reading the input and the code that validates the input. Also, if you prefer to encapsulate the validation code within the same method, you can use delegates. See below.
Func<string,bool> InputIsInvalid = (stringNum) =>
{
int intNum;
return !int.TryParse(stringNum, out intNum) || intNum <= 0 || intNum > 2000;
};
while(InputIsInvalid(Console.ReadLine()))
{
Console.WriteLine("There is an error in the input value");
}
Create a middle exit loop with an infinite for and break to test only once:
string snum;
int num;
for (;;) {
snum = Console.ReadLine();
if (Int32.TryParse(snum, out num) && 0 <= num && num <= 2000)
break;
Console.Write("There is an error in the input value");
}
I´m having problems with getting my code to work while using TryParse to catch if the user where to input a string instead of a int. If I use it as it looks now I only get the base value of 0 if something other than an int is input. I want it to show an error message to the user.
Have tried messing around with a number of different ways of using TryParse but none of them has really been helpfull.
static void Main(string[] args)
{
Random r = new Random();
int speltal = r.Next(1,21);
bool play = false;
int myNum;
while (!play)
{
Console.Write("\n\tGuess a number between 1 and 20: ");
Int32.TryParse(Console.ReadLine(), out myNum);
if (myNum < guessNum)
{
Console.WriteLine("\tThe number you have guessed is to low");
Console.ReadLine();
}
if (myNum > guessNum)
{
Console.WriteLine("\tThe number you have guessed is to high");
Console.ReadLine();
}
if (myNum == guessNum)
{
Console.WriteLine("\tCongratulations you guessed the right number!");
Console.ReadLine();
}
I want it show an error message to the user if they put in anything other than a int. It also have to include TryParse according to my teatcher
You're not capturing the bool output of TryParse so you have no idea if a non-numeric value was entered. Try something like this:
bool isValid;
do
{
Console.Write("\n\tGuess a number between 1 and 20: ");
isValid = Int32.TryParse(Console.ReadLine(), out myNum);
if(!isValid)
{
Console.WriteLine("\n\tInvalid input detected. Please try again.");
}
} while(!isValid)
The TryParse method can only put integers in the passed variable (as it is of type int), so if the value passed to it can't be parsed into an integer, the default value of int (0) will be assigned to the variable.
The way TryParse tell you if it successfully parsed the number or not, is by returning a boolean indicator.
You can try this:
while (true)
{
bool valid = int.TryParse(Console.ReadLine(), out myNum);
if(valid)
break;
Console.WriteLine("Input invalid. Please try again");
}
TryParse returns a Boolean which indicates if the input string was successfully parsed or not. Both of the answers above are correct on how to handle a invalid input but, here is a cleaner version which will also uphold the rule, between 1 and 20:
while (true)
{
Console.Write("\n\tGuess a number between 1 and 20: ");
//Checks to see if the input was successfully parsed to a integer also, performs a Trim on the input as to remove any accidental white spaces that a user might have typed in, e.g. "1000 "
if (int.TryParse(Console.ReadLine().Trim(), out myNum))
{
//Checks to see if the parsed number is in the specified range
if ((myNum > 0) && (myNum < 21))
{
break;
}
Console.WriteLine("\tThe input number was out of the specified range.");
}
else
{
Console.WriteLine("\tFailed to parse the input text.");
}
//Optional, makes the thread sleep so the user has the time to read the error message.
Thread.Sleep(1500);
//Optional, clears the console as to not create duplicates of the error message and the value of Console.Write
Console.Clear();
}
// Continue here, if (myNum < guessNum) . . .
You should use the bool returned by TryParse. Something that looks like this:
Updated answer:
static void Main(string[] args)
{
Random random = new Random();
int guessNum = random.Next(1, 21);
while(true)
{
Console.WriteLine("Guess the number between 1 and 21.");
if (Int32.TryParse(Console.ReadLine(), out int input))
{
if (input == guessNum)
{
Console.WriteLine($"You guessed it right. The number is {input}");
if(ShouldContinue())
{
guessNum = random.Next();
continue;
}
else
{
break;
}
}
if (input < guessNum)
Console.WriteLine("The number you guessed is smaller.");
else
Console.WriteLine("The number you guessed is bigger");
}
else
{
Console.WriteLine("Please enter a number between 1 and 21 as your guess");
}
}
}
static bool ShouldContinue()
{
while (true)
{
Console.WriteLine($"Do you want to continue playing? (y/n)");
string continueInput = Console.ReadLine().Trim().ToLower();
if (continueInput == "y")
return true;
else if (continueInput == "n")
return false;
else
Console.WriteLine("Invalid input!. Please choose 'y' or 'n'.");
}
}
Old answer:
while (true)
{
if (Int32.TryParse(inputInt, out int myNum))
{
// your logic goes here, too low/high or correct answer.
}
}
I have public string method with an if/else statement. When I don't put a return keyword on the else, I get the error that not all code paths return a value but when I add the return to the else statement, I get an Use of unassigned local variable 'result'. When I do return "Please enter a valid number";, nothing displays on the console when I type in any letter. I need to let the user know that they entered something in that couldn't be converted into an integer.
public string AddNumbers(string userInputString)
{
int result;
int num2 = RandomNumberInt();
bool isTrue = int.TryParse(userInputString, out int num1);
if (isTrue == true)
{
result = num1 + num2;
Console.WriteLine("Adding your number and a random number, please wait...");
Thread.Sleep(1000);
Console.WriteLine("{0} + {1} = {2}", num1, num2, result);
isTrue = true;
return result.ToString();
}
else
{
return "Please enter a valid number";
}
}
It's because your method is asking for a return. But since you have an if, let's put it this way
Team Leader: Hey bob I want you to finish this job.
In here you are expecting that bob will finish your job but you put a condition
You: If I can go to office today sir.
since you have an If condition, what if you can't go today? Does it mean you can't finish the job tomorrow and any other day? That's why it says not all code paths return a value because you never gave other/default value
Going back in your code, you ask
if (isTrue == true)
{
result = num1 + num2;
Console.WriteLine("Adding your number and a random number, please wait...");
Thread.Sleep(1000);
Console.WriteLine("{0} + {1} = {2}", num1, num2, result);
isTrue = true;
return result.ToString();
}
but what if it is not true, then it will go to else. You can set int result = 0 so it is defined from start when else run and it will not return an error of unassigned local variable.
public string myMethod()
{
int result = 0; //This must have a default value so in else part it is not unassigned when you return.
int num2 = RandomNumberInt();
bool isTrue = int.TryParse(userInputString, out int num1);
if(isTrue)
{
//do something in result here
return result.toString(); //This will return your in value as string
}
else
{
return "Your message as string" // This will return any string to provide for string return of the method
}
}
Your problem regarding not displaying the string "Please enter a valid number" is a different issue. You have to post also what method calls the AddNumbers method that will use the returned string. For use the problem is in that method because your if and else is in correct format;
Whenever you get confused by application logic, it is often helpful to break the logic down into pieces. This gives you an opportunity to think through the problem and decide how the tasks add up to give you the final result.
Start at a high level and sketch out the overall flow:
static public void MethodNameThatDescribesThisActivity()
{
var userResponse = ReadIntegerFromConsole("Please enter an integer.");
var randomNumber = RandomNumberInt();
DisplaySum(userResponse, randomNumber, 1000);
}
Then implement the pieces:
static public int ReadIntegerFromConsole(string prompt)
{
int result;
while (true)
{
Console.WriteLine(prompt);
var input = Console.ReadLine();
var ok = int.TryParse(input, out result);
if (ok) break;
Console.WriteLine("That isn't a valid integer.");
}
return result;
}
static public void DisplaySum(int userNumber, int randomNumber, int delay)
{
var sum = userNumber + randomNumber;
Thread.Sleep(delay);
Console.WriteLine("The total of {0} + {1} = {2}", userNumber, randomNumber, sum);
}
If you do it this way, it often solves the logic problem for you. And it also makes your code easier to read.