edit: for those who have answered, I apologize, I should have been more clear, the assignment REQUIRES use of the for loop per my professor.
I'm doing a small assignment for class and am having trouble breaking out of a for loop and prompting the user to enter a valid value. My code is set up thus far as:
const int MINRANGE = 1;
const int MAXRANGE = 20;
int input = 0;
Console.Write("Enter the desired maximum: ");
string strInput = Console.ReadLine();
Console.WriteLine("\n\n\n");
for (int.TryParse(strInput, out input); input >= MINRANGE && input <= MAXRANGE; input--)
{
Console.WriteLine("{0,2} {1,5}", input, Math.Pow(input, 3));
}
The program displays everything I need it to correctly. When the user enters a value out of the range I have specified, I need to give them a short message and then break out of the loop and return to the beginning prompt. I think I need to use something like the following if statement:
if (input >= MAXRANGE || input <= MINRANGE)
{
Console.WriteLine("That is not a valid value, please try again.");
}
Perhaps with a break; following it? But I'm not sure how to use it inside of the for loop. I've tried placing it outside, but that doesn't get me back to the user prompt, but neither does placing it inside the loop, so I'm obviously doing something wrong.
You can use a while loop
int input;
while(!int.TryParse(Console.ReadLine(), out input) || input >= MAXRANGE)
{
Console.WriteLine("Not valid!");
}
Note that this may get the user "stuck" and a helpful message as to why it isn't valid would be nice
If for some bizarre reason you must use a for loop you can use the following but it is horrible code that I would never condone
int input;
for(;;)
{
if(int.TryParse(Console.ReadLine(), out input) && input < MAXRANGE)
break;
}
Its better to do the validation before entering the loop. Try this out.....
const int MINRANGE = 1;
const int MAXRANGE = 20;
int input = 0;
Console.Write("Enter the desired maximum: ");
string strInput = Console.ReadLine();
Console.WriteLine("\n\n\n");
if (input > MAXRANGE || input < MINRANGE)
{
Console.WriteLine("That is not a valid value, please try again.");
}
else
{
for (int.TryParse(strInput, out input); input >= MINRANGE && input <=
MAXRANGE; input--)
{
Console.WriteLine("{0,2} {1,3}", input, Math.Pow(input, 3));
}
}
I would rewrite your code as follows. Creating a method for asking the input:
const int MINRANGE = 1;
const int MAXRANGE = 20;
int input = 0;
string strInput = AskInput();
while (!int.TryParse(strInput, out input)) /*while the number is invalid*/
{
Console.WriteLine("Your input is invalid. Try again.");
strInput = AskInput();
}
while (input >= MINRANGE && input <= MAXRANGE)
{
Console.WriteLine("{0,2} {1,3}", input, Math.Pow(input, 3));
input--;
}
Where AskInput is:
private static string AskInput()
{
Console.Write("Enter the desired maximum: ");
string strInput = Console.ReadLine();
Console.WriteLine("\n\n\n");
return strInput;
}
for ([(fist) Initialization];
[(second)Condition];
[(third or exit the loop) Progression])
{
[(fourth) Loop's body -if we reached third than we got here ]
}
The for loop is constructed of three parts:
The initialization part which happens only once when the loop starts.
The condition evaluation part which happens for every iteration.
The indexer progression part which also happens for every loop.
The order is as follows:
Start Loop => init => CheckCondition => if OK Progress the indexer and execute loop's body, else the loop is done.
The initialization part happens just once, if you want it to happen foreach interation it should be inside the loop or in the conditional section of the loop instead.
Best practice would be to use a while loop when the number of iterations is unknown ahead, like in this case, when it's determined by user's input.
Related
I am not sure how to tackle this problem. I tried putting the do while loop in the method GetUserInput and then putting the for loop in the do while loop. It doesn't reset the question it just takes the number and adds it the numbers before it. Its a supposed to be a calculator program.
//This propgram will be used to make a calculator for the class project.
//The numbers are stored as floats as well as the result. Then displayed on console.
//V1 adds a do-while loop that repeats as long as the user wants.
//V2 adds a if and else logic for when the user input a character other than a number the program will close.
//V3 added a for-loop to increase the amount of numbers that can be considered in the calculation. It makes an array
//V4 added methods to get user input and sum the numbers
class MainClass
{
public static void Main(string[] args)
{
Console.WriteLine("Hello Ulises Sanchez");
//Define 3 floating point numbers to capture the 2 inputs and the result
//floats are used to capture a broader range of numbers
float[] userInput = new float[10];
//stores the number of inputs the user requests
int numberOfUserInputs;
//define strings to store data read and also user prompts
string inputString;
string doMorefunctions = "Add More Numbers Together - y = yes - anything else for no";
//variable to test the condition to continue with calculations
bool moreActions;
do
{
Console.Clear();
numberOfUserInputs = GetuserInput(userInput);
//adds the numbers together
Summation(userInput, numberOfUserInputs);
//reset moreAction
moreActions = false;
Console.WriteLine(doMorefunctions);
inputString = Console.ReadLine();
if (inputString == "y" || inputString == "Y")
moreActions = true;
} while (moreActions);
}
//Gets the number of user inputs and stores each in the userInput array
static int GetuserInput(float[] inputArray)
{
int numberOfInputs;
string userInputPrompt = "How many numbers do you want to enter?";
//string continueMessage = "Hit any key to continue";
string errorMessage = "Invalid Input";
string inputString;
bool TryAgain;
Array.Clear(inputArray, 0, 10);
//Gets number of inputs from user
Console.Write(userInputPrompt);
inputString = Console.ReadLine();
numberOfInputs = int.Parse(inputString);
//Get inputs
for (int i = 0; i < numberOfInputs; i++)
{
Console.Write("Enter variable number {0}: ", i + 1);
inputString = Console.ReadLine();
if (Single.TryParse(inputString, out float result))
{
//if input is valid convert to float
inputArray[i] = float.Parse(inputString);
}
else
{
TryAgain = false;
Console.WriteLine(errorMessage);
inputString = Console.ReadLine();
if (inputString == "y" || inputString == "Y") TryAgain = true;
//if input is not valid input exit program
//Console.WriteLine(continueMessage);
//Console.ReadLine();
//System.Environment.Exit(1);
}
}
return numberOfInputs;
}
//takes the user input and performs a summation calculation
static void Summation(float[] inputArray, int numberOfInputs)
{
float summationResult = 0.0f;
for (int i = 0; i < numberOfInputs; i++)
{
summationResult += inputArray[i];
}
//display result to the screen
Console.WriteLine("Summation = {0}", summationResult);
}
}
We have this concept of "don't repeat yourself" (DRY) so we look for ways to make code that repeats itself not do so. Every one of your methods repeats the print/ReadLine process for asking a question
Let's have a method that asks the user for a string:
public string Ask(string q){
Console.WriteLine(q);
return Console.ReadLine();
}
Now we can say:
string name = Ask("what is your name? ");
Suppose blank input is invalid, let's use a loop to repeat the question:
public string Ask(string q){
string a = "";
while(string.IsNullOrEmpty(a)){
Console.WriteLine(q);
a = Console.ReadLine();
}
return a;
}
If the user gives no answer, they are stuck in the loop and the question is repeated until they give a valid answer
Now let's reuse this to ask for an int:
public int AskInt(string q){
return int.Parse(Ask(q));
}
Here we reuse Ask within AskInt so we don't do the print/read thing again and we leverage the "cannot renter blank" validation we already write
This however explodes if the user enters non ints
So let's use int.TryParse and keep looping while they enter garbage that doesn't parse;
public int AskInt(string q){
bool success = false;
into a=0;
while(!success){
success = int.TryParse(Ask(q), out a);
}
return a;
}
The user can only get to the last line if they enter an int
If you also want to add range validation, for example, you can put an int min, int max into your method parameters and inside the loop do success = success && a <= && a >= min
int guess = AskInt("enter a number between 1 and 10: ", 1, 10);
The idea is to write one method that does one thing really well I.e. "ask the user for a string" and then reuse that when we write the next method that does one thing well, so we end up with two methods that do two things well. Giving the methods a sensible name allows us to package up that bit of logic they do into a few words and make out code read like a book. It doesn't need as many comments then
//ask the user what their next guess is
int guess = AskInt("enter a number between 1 and 10: ", 1, 10);
This comment isn't needed; we can easily deduce the same just by reading the code.
This question already has answers here:
check for valid number input - console application
(5 answers)
Allow To Only Input A Number - C#
(1 answer)
Closed 2 years ago.
I have just started a table programme. I am just a trainee learning C# from internet, so I am not so good in this.
I just wanted the programme to run according to the user. I want that if the user hits enter simply, the programme should not crash. That is I just wanted to know how to prevent null enter. This is the code is used:
The "______" which used if for writing a line
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace tables
{
class Program
{
static void Main(string[] args)
{
goto found;
found:
Console.WriteLine("");
string textToEnter = "MULTIPLATION TABLES";
Console.WriteLine(String.Format("{0," + ((Console.WindowWidth / 2) + (textToEnter.Length / 2)) + "}", textToEnter));
Console.WriteLine("");
Console.WriteLine("________________________________________________________________________________");
Console.WriteLine("");
int num, j, i;
Console.Write("enter the number of which table u need ? :- ");
num = Convert.ToInt32( Console.ReadLine());
while (num == 0)
{
Console.WriteLine("please enter a valid input");
Console.Write("enter the number of which table u need ? :- ");
num = Convert.ToInt32(Console.ReadLine());
}
Console.Write("enter the number till which the table need to be ? :- ");
j = Convert.ToInt32(Console.ReadLine());
while (j == 0)
{
Console.WriteLine("please enter a valid input");
Console.Write("enter the number till which the table need to be ? :- ");
j = Convert.ToInt32(Console.ReadLine());
}
i = Convert.ToInt32(j);
for (j=1; ; j++)
{
if (j > i)
{
break;
}
Console.WriteLine(num + " * " + j + " = " + num * j);
}
string str;
Console.Write("do you want to continue? (y/n) :- " );
str= Console.ReadLine();
foreach (char ch in str)
{
if (ch == 'y')
{
goto found;
}
else if (ch=='n' )
{
Console.WriteLine("");
Console.WriteLine("THANK YOU FOR USING MY PRODUCT");
}
else
{
Console.WriteLine("please enter a valid input");
}
}
Console.ReadKey();
}
}
}
As suggested in the comments, I'd use int.TryParse(), but inside a do...while() loop. Use a separate flag (boolean) to track whether the user should keep trying again:
bool invalid;
int num, j, i;
do
{
invalid = true;
Console.Write("enter the number of which table u need ? :- ");
String response = Console.ReadLine();
if (int.TryParse(response, out num))
{
invalid = false;
}
else
{
Console.WriteLine("Invalid input. Please try again.");
}
} while (invalid);
// ...repeat the above do...while() block for "j" and "i"...
When you're accepting user input, it's important to perform validation on it. You can't assume that the user will always enter correctly formatted data that your program will be able to work with. As you discovered, a user who hits enter will give you an empty string (""), which can't be parsed to anything.
C# has several ways of attempting parsing. The first, which you're using, is Convert.ToInt32(), which throws an exception if the input it receives is not, in fact, a number. You have to catch the exception with a try/catch block, like so:
try
{
num = Convert.ToInt32(Console.ReadLine());
}
catch(FormatException ex)
{
Console.WriteLine("You didn't enter a proper number!");
}
However, in general, exceptions should be, well, exceptional. They should only be relied upon when rare failures occur, because unwinding the call stack can be expensive.
I would argue that C# has a better method for you to use in this instance: Int32.TryParse()
You can see the documentation here.
TryParse takes two parameters, the thing you're trying to parse (convert), and then a number to store the value in. It returns true or false, indicating if it succeeded or failed in converting the number.
You might use it like this:
var success = Int32.TryParse(Console.ReadLine(), num);
if (success)
{
// do something with 'num' -- it has a valid value now.
}
else
{
// Warn the user, perhaps prompt them to try again
Console.WriteLine("That wasn't a valid number!");
}
You can use a methode to get a safe int value:
private static int ReadIntValue(string psMessage)
{
int lnInt;
string lsValue = string.Empty;
do
{
Console.Write(psMessage);
lsValue = Console.ReadLine();
} while (!int.TryParse(lsValue, out lnInt));
return lnInt;
}
And then use this:
num = ReadIntValue("enter the number of which table u need ? :- ");
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'm new to C# and programming as a whole and i have a quick question to ask you guys, I've searched a bit but only found far too complicated examples for me to implement in my work so here goes:
int[] newArray = new int[7];
Console.WriteLine("Hello! Please enter 7 numbers between 1-25, press ENTER after each number. ");
for (int i = 0; i < newArray.Length; i++)
bool loop = true;
do
{
try
{
newArray[i] = Convert.ToInt32(Console.ReadLine());
loop = false;
}
catch
{
Console.WriteLine("You may only enter numbers!");
}
} while (loop);
Console.Write("You entered the following numbers: ");
for (int i = 0; i < newArray.Length; i++)
{
Console.WriteLine(newArray[i]);
}
}
This is the first part of a bingogame im trying to write, but i can't understand why the names loop and i don't exist, should i make something static? Move some brackets around? Please help.
You need to wrap the entire for statement in braces, otherwise it will only execute the next line of code, which is just bool loop = true;.
for (int i = 0; i < newArray.Length; i++)
{ // <-- Add this
bool loop = true;
do
{
try
{
newArray[i] = Convert.ToInt32(Console.ReadLine());
loop = false;
}
catch
{
Console.WriteLine("You may only enter numbers!");
}
} while (loop);
Console.Write("You entered the following numbers: ");
}
It's worth to mention about string.Join method to print all elements of the list.
Console.WriteLine("You entered the following numbers: ");
Console.WriteLine(string.Join(", ", newArray));
After using Parse/TryParse method, you don't need to use Convert.ToInt32 any more.
To validate number and be able to reenter it, it is much better to do 2 IF statements instead of using Constains method of Enumerable class.
while (!int.TryParse(Console.ReadLine(), out number) || number < 1 || number > 25)
{
Console.WriteLine("You may only enter numbers from range 1-25!");
}
Make one single bracket right after your for cycle.
You're missing an open brace. This looks like homework so I'm not going to rewrite it for you. Take a closer look and work on the formatting and indentations. That will give you a clue as to were that missing brace should be.
Here is a nicer way to test for number input without the try/catch
var newArray = new int[7];
Console.WriteLine("Hello! Please enter 7 numbers between 1-25, press ENTER after each number. ");
for (var i = 0; i <= newArray.Length - 1; i++)
{
int number;
while (!int.TryParse(Console.ReadLine(), out number))
{
Console.WriteLine("You may only enter numbers!");
}
newArray[i] = Convert.ToInt32(number);
}
Console.WriteLine("You entered the following numbers: ");
foreach (var t in newArray)
{
Console.WriteLine(t);
}
I am new to C# and was doing this program as an exercise. I have managed to get my program to print the reversed number of the input given by the user, but when I move onto checking whether it is a palindrome or not, it does not calculate the answer correctly. It always prints 'not a palindrome'.
After some error checking, I realized that the reason why it was doing this is because the last number that gets stored in newnum is just the last digit after being reversed and not the entire number. How can I rectify this??
My Code
int i, remainder = 0, newnum = 0;
Console.WriteLine("Enter a Number: ");
int uinput = Convert.ToInt32((Console.ReadLine()));
for (i = uinput; i > 0; i = (i / 10))
{
remainder = i % 10;
Console.Write(remainder);
newnum = remainder;
}
if (newnum == uinput)
{
Console.WriteLine("The Number {0} is a palindrome", uinput);
}
else
{
Console.WriteLine("Number is not a palidrome");
}
Console.WriteLine(uinput);
Console.WriteLine(newnum);
Console.ReadKey();
}
I also looked online at another code example, but the thing I don't understand in that is why num is being converted to boolean type in the while loop? Is that just to keep the loop running?
The Code reffered to above
int num, rem, sum = 0, temp;
//clrscr();
Console.WriteLine("\n >>>> To Find a Number is Palindrome or not <<<< ");
Console.Write("\n Enter a number: ");
num = Convert.ToInt32(Console.ReadLine());
temp = num;
while (Convert.ToBoolean(num))
{
rem = num % 10; //for getting remainder by dividing with 10
num = num / 10; //for getting quotient by dividing with 10
sum = sum * 10 + rem; /*multiplying the sum with 10 and adding
remainder*/
}
Console.WriteLine("\n The Reversed Number is: {0} \n", sum);
if (temp == sum) //checking whether the reversed number is equal to entered number
{
Console.WriteLine("\n Number is Palindrome \n\n");
}
else
{
Console.WriteLine("\n Number is not a palindrome \n\n");
}
Console.ReadLine();
Any sort of help is much appreciated!! Thank You :)
I'm not sure what you're asking, since the second snippet of code you found online should fix your issue.
Your code works, if you just change the line
newnum = remainder;
to
newnum = (newnum*10) + remainder;
The issue in your case is not the condition you used in the for loop, it's just that you're overwriting newnum with the remainder every time, so newnum is only storing the last reminder that was calculated in the loop, "forgetting" all the others it had calculated before.
To reverse the number, every time you enter the loop, you should add the last remainder you've found to the right of newnum, which is effectively equivalent to multiplying everything by 10 and adding remainder.
Try to follow it step by step with pen and paper (or with a debugger).
public bool isPalindome(int num)
{
string sNum = num.ToString();
for (int i = 0; i<sNum.Length; i++)
if (sNum[i] != sNum[sNum.Length-1-i]) return false;
return true;
}
I think that will do it... Untested!!
As dognose (and Eren) correctly assert you only need to go halfway through
public bool isPalindome(int num)
{
string sNum = num.ToString();
for (int i = 0; i < sNum.Length/2; i++)
if (sNum[i] != sNum[sNum.Length-1-i]) return false;
return true;
}
You will also need to decide what happend to negative numbers.. ie is -121 a plaindome? This method will say that it isn't...
Easiest way:
public static Boolean isPalindrom(Int32 number){
char[] n1 = number.ToString().ToCharArray();
char[] n2 = number.ToString().ToCharArray();
Array.Reverse(n2);
String s1 = new String(n1);
String s2 = new String(n2);
return (s1 == s2);
}
https://dotnetfiddle.net/HQduT5
you could also use Integers for s1 and s2 and return (s1-s2 == 0)
You have many ways of accomplish this exercise.
A. You can leave the input as string and loop it over, every iteration to check if the value of index 'i' and value of index 'len-i-1' are equals, if not false, otherwise return at the end of the loop true. (the loop should run till i < len/2)
B. You can create a new string and insert the text from end to start and then compare if the original string and result string are equals.
C. there are much more ways without using the string solutions, just with calculation..
int x;
cin<<x; //input the number
int ar[];
int i=0;
temp2=0;
while(x/10 != 0)
{
int temp=x%10;
ar[i]=temp;
x=x/10;
i++;
}
for(int j=0, j<i,j++)
{
temp2=temp2*10+ar[j];
}
if(temp2==x){cout<<"palindrome"}
else {"not palindrome"}
ok here is the logic:
we first input the number x(it can be of any length)..Next we split the number into array..the condition to do this is tha we check for the qoutient to decide whether the number is fully split..next we take the array and rejoin it and check with the input number..
Use the following code:
public boolean isPalindrom(Integer number)
{
return number.Equals(int.Parse(String.Join("", String.Join("", number.ToString().ToCharArray().Reverse().ToArray()))));
}