I'm a novice when it comes to programing. I'm working on a sort of grocery shopping list. I have a string list, where the user can add groceries to:
List<string> list = new List<string>();
Now if the user wants to remove a certain object(grocery) in the list i would like him to do it with numbers instead of typing in the grocery name in the console window, which i have accomplished here:
case 2:
Console.WriteLine("What would you like to remove from the list?");
int removeGroc = Convert.ToInt32(Console.ReadLine());
list.RemoveAt(removeGroc);
break;
What I want to do is make sure to check that if the user enters for example number 5 but there are only 3 objects in the list, so the user will be asked to enter a number again since there are only 3 objects in the list(0, 1 and 2). I've searched everywhere and tried different things but they don't seem to work or my knowledge is to bad to understand it. So how would i go about doing this? I have a jist of what i need to do but I dont know how to do it. I'm thinking that i need to find the "id" of the list and then check if it exists, but I can't seem to find how to do this online.
Here is the edit which worked thanks to the comments if any other novice sees this:
Console.WriteLine("What would you like to remove from the list?");
var removeGroc = Console.ReadLine();
int removeGrocId;
bool parseSuccess = int.TryParse(removeGroc, out removeGrocId);
if (removeGrocId < list.Count)
list.RemoveAt(removeGrocId);
else
Console.WriteLine("Write a valid number!");
You can do it with
list.Count; //return the number of the items in the list
So you validate it with the number of the items in the list:
if(removeGroc > listCount){ //do someting }
I've found it really useful to use a helper method that will get a number from the user. This method uses TryParse to convert the input to a number, which is really handy because it returns a bool that indicates success, and then the converted number is set to an out parameter. Note that in your method above, if the user enters an invalid number, like "two", it will throw an exception.
The method below also takes in an optional string "prompt", which is displayed to the user, and then it loops until they enter a valid value:
private static int GetIntFromUser(string prompt)
{
int input;
do
{
Console.Write(prompt);
} while (!int.TryParse(Console.ReadLine(), out input));
return input;
}
Now, to get an integer from the user, we would just do:
int removeGroc = GetIntFromUser("What would you like to remove from the list?");
This can be improved slightly by adding a feature where instead of asking the question again in a new line (which can slowly eat up the console window space if they keep entering incorrect data), we can use the Console.CursorTop and Console.SetCursorPosition to overwrite the current line with blank spaces (clearing their original input) and then write the question again on the same line:
private static int GetIntFromUser(string prompt)
{
int result;
var cursorTop = Console.CursorTop;
do
{
// Set the cursor to the beginning of the line,
// write a blank line, and set it to the beginning again
Console.SetCursorPosition(0, cursorTop);
Console.Write(new string(' ', Console.WindowWidth));
Console.SetCursorPosition(0, cursorTop);
Console.Write(prompt);
} while (!int.TryParse(Console.ReadLine(), out result));
return result;
}
Alright, now we just need to add a way to specify valid entries, so that if they enter a number but it's not valid for our scenario, it will continue to ask them for valid input.
The first thing I did was write a bunch of overloads of this method that took in things like minValue, maxValue, even a List<int> validNumbers and List<int> invalidNumbers, and then had logic to check if the number they entered met all these criteria.
But since we have the ability to pass a function to a method, I opted instead to just let the client pass in their own validation function that takes in an int and returns a bool. This way the same method can be re-used for all kinds of scenarios:
private static int GetIntFromUser(string prompt, Func<int, bool> validator = null)
{
int result;
var cursorTop = Console.CursorTop;
do
{
Console.SetCursorPosition(0, cursorTop);
Console.Write(new string(' ', Console.WindowWidth));
Console.SetCursorPosition(0, cursorTop);
Console.Write(prompt);
} while (!int.TryParse(Console.ReadLine(), out result) ||
(validator != null && !validator.Invoke(result)));
return result;
}
Now we have a method that will take any type of validation we want, and will apply it to the user input. For your example, the requirements are that the number is greater than or equal to 0, and less than or equal to list.Count - 1 (to get a valid index in the list). This can be written as a lambda method like:
i => i >= 0 && i <= list.Count - 1
So, applying this to your example, we can now simply do something like:
case 2:
{
int minVal = 0;
int maxVal = list.Count - 1;
int removeGroc = GetIntFromUser($"Enter the item to remove ({minVal} - {maxVal}): ",
i => i >= minVal && i <= maxVal);
list.RemoveAt(removeGroc);
break;
}
Related
I'm new to C# and i would really need your help with a project.
The idea is to ask the user for 10 numbers between 1-20. The numbers that the user enters are stored in an array. In the next phase a random number i generated and then the program compare all the numbers that the user previously entered with the random number. If one of numbers matches the program write something like "You win!".
My current solution is okay and working but I want a better exception handling than the current one. Here is my problem:
As you can see in my code below I rely on a loop and try/catch to ensure that the user enters a valid number, but after testing several times I discovered that if you enter a valid input, let say the first time but not the second, the unvalid input is still sent to the for-loop and to the next index.
I want to ensure that the user enters a valid number and if not the for-loop would temporarily "pause" until the next VALID number is entered.
bool start = true; //Create a loop.
{
while (start == true)
{
try
{
for (int x = 0; x < vektor.Length; x++) //To fill my array.
{
Console.WriteLine("Enter a number between 1 and 20:");
vektor[x] = int.Parse(Console.ReadLine());
start = false;
}
}
catch
{
Console.WriteLine("Error, you need to enter a number!");
}
}
}
Make a method that asks the user a question and doesn't give an answer until it's valid:
public int Ask(string question, int lower, int upper){
while(true)
{
Console.WriteLine(question);
string input = Console.ReadLine();
bool valid = int.TryParse(input, out int inputInt); //valid is true if it was a number
valid = valid && inputInt >= lower && inputInt <= upper; //but also test was it in range?
if(valid)
return inputInt; //if not valid, repeat the question because the loop is infinite
}
}
valid will be true if the user enters a number, but if they entered 40 for a 1 to 20 range, then the second validity assessment is:
valid = true /*it was a number*/ && true /*40 is >= 1*/ && false /*40 is not <= 20*/
So valid becomes false. We can only escape the Ask() method, returning the valid number if valid is true, otherwise the loop goes round again
--
Now you can have a list of numbers, say you want 10, we can loop and add numbers to a list until we get 10:
List<int> numbers = new List<int>();
while(numbers.Count < 10)
{
int validNumber = Ask("Enter a nubmer between 1 and 20: ", 1, 20);
numbers.Add(validNumber);
}
You can do this as an array if you like:
int[] numbers = new int[10];
for(int x = 0; x<numbers.length; x++)
{
int validNumber = Ask("Enter a nubmer between 1 and 20: ", 1, 20);
numbers[x] = validNumber;
}
Because you know that the Ask method will never return unless the input is valid, so the loop "pauses"
I have some code below that is almost finished, but the last thing I want to do is for the console app to display the number they have gotten from the user
EX: if user input 1, 3, 5
the console will display
The number you have inserted are:
One
Three
Five
Is it possible to do that ?
Thanks
static void Main (string []args)
{
string again;
do
{
Console.Clear();
Console.WriteLine("Insert Random number");
int number = int.Parse(Console.ReadLine());
Console.WriteLine("Would you like to Insert another number ?(Enter Y for yes /Enter any other key to exit)");
again = Console.ReadLine();
} while (again == "Y");
Console.WriteLine("The number you have inserted are: ");
Console.ReadKey();
}
First, you need a place to keep all the numbers you collected. Given this code, you may be expected to use an array, but real code is more likely to use a generic List<int>. Declare it near the beginning of the Main method like this:
List<int> numbers = new List<int>();
Add each number to it after Parse()-ing like this:
numbers.Add(number);
Then, in between the final WriteLine() and ReadKey() calls, you need to loop through the collected numbers:
int i = 0;
for (int i = 0; i < numbers.Length; i++)
{
Console.WriteLine($"{i+1}. {numbers[i]}");
}
What you won't be able to do in a simple way is convert the digit 1 to the text value One. There's nothing built into C# or .Net to do that part for you. Since this code looks like a learning exercise, I'll leave you to attempt that part on your own.
I am writing a method to take user input for a menu with three options: 1,2,3. My do while loop runs, however my while logic is still accepting unwanted input. Why is my code not looping for inputs outside of my set range of values?
I have tried different logical operators, removing logical operators and setting while Option < Value.
private static MenuOption ReadUserOption()
{
int Option;
Console.WriteLine("Please make a selection");
Console.WriteLine("1, will run TestName, 2 will run Guess that number, 3 Wil quit the program.");
do
{
Option = Convert.ToInt32(Console.ReadLine());
return (MenuOption)(Option - 1);
} while (Option < 1 || Option > 3);
}
My goal is for any user input outside of <1 and >3 for the loop to continue until a value within that range is entered. In its current state if I enter 0 the loop will accept that value and output -1.
You just need to move the return statement outside the loop
private static MenuOption ReadUserOption()
{
int Option;
Console.WriteLine("Please make a selection");
Console.WriteLine("1, will run TestName, 2 will run Guess that number, 3 Wil quit the program.");
do
{
Option = Convert.ToInt32(Console.ReadLine());
} while (Option < 1 || Option > 3);
return (MenuOption)(Option - 1);
}
There is something wrong with my code. I am teaching myself c# and one of the challenges in this chapter was to prompt the user for 10 numbers, store them in an array, than ask for 1 additional number. Then the program would say whether the additional number matched one of the numbers in the array. Now what I have below does work, but only if I enter in a comparison number that is less than 10 which is the size of the array.
I'm not sure how to fix it. I am not sure how to do the comparison. I tried a FOR loop first which kind of worked, but ran through the loop and displayed the comparison against all 10 numbers so you would get 9 lines of No! and 1 line of Yes!. I put in a break; which stopped it counting all 10 but if I entered the number 5 for comparison, then I would get 4 lines of No! and 1 of Yes!. The below has been the only way I could get it to work reliably but only as long as the number isn't out of the bounds of the array.
I can see why I get the error when the number is above 10, I just don't know what to use to compare it but still allow the user to enter in any valid integer. Any assistance would be great!
int[] myNum = new int[10];
Console.WriteLine("Starting program ...");
Console.WriteLine("Please enter 10 numbers.");
for (int i = 0; i <= 9; ++i)
{
Console.Write("Number {0}: ", i + 1);
myNum[i] = Int32.Parse(Console.ReadLine());
}
Console.WriteLine("Thank you. You entered the numbers ");
foreach (int i in myNum)
{
Console.Write("{0} ", i);
}
Console.WriteLine("");
Console.Write("Please enter 1 additional number: ");
int myChoice = Int32.Parse(Console.ReadLine());
Console.WriteLine("Thank you. You entered the number {0}.", myChoice);
int compareArray = myNum[myChoice - 1];
if (compareArray == myChoice)
{
Console.WriteLine("Yes! The number {0} is equal to one of the numbers you previously entered.", myChoice);
}
else
{
Console.WriteLine("No! The number {0} is not equal to any of the entered numbers.", myChoice);
}
Console.WriteLine("End program ...");
Console.ReadLine();
You were on the right track- you want to loop through the array in myNum and compare each element to the variable myChoice. If you don't want to print whether each element of the array is a match, create a new variable and use it to keep track of whether you've found a match or not. Then after the loop you can check that variable and print your finding. You'd usually use a bool variable for that- set it false to start, then true when you find a match.
bool foundMatch = false;
for (int i = 0; i < 10; i++) {
if (myNum[i] == myChoice) {
foundMatch = true;
}
}
if (foundMatch) {
Console.WriteLine("Yes! The number {0} is equal to one of the numbers you previously entered.", myChoice);
}
If you include the System.Linq namespace (or if you change the type of myNum to be something that implements ICollection<T>, like List<T>), you can use myNum.Contains(myChoice) to see if the value myChoice matches one of the values in myNum. array.Contains returns a boolean that is true if the specified value is found in the array and false if it is not.
You can update your code to use this like so:
//int compareArray = myNum[myChoice - 1]; // This line is no longer needed
if (myNum.Contains(myChoice))
{
Console.WriteLine("Yes! The number {0} is equal to one of the numbers you previously entered.", myChoice);
}
else
{
Console.WriteLine("No! The number {0} is not equal to any of the entered numbers.", myChoice);
}
If you're looking for numbers that are definitely between 1 and 10, then before you use
int compareArray = myNum[myChoice - 1];
check if it's over the value of 10. For example:
while(myChoice > 10)
{
Console.Write("Please choose a number less than or equal to 10: ");
myChoice = Int32.Parse(Console.ReadLine());
}
The benefit of putting it inside a while loop instead of an if tag means that, when the user enters another number, the value of myChoice will be rewritten, and compared against. If they enter a number over 10, it'll keep responding Please choose a number less than or equal to 10. until the number they input is below or equal to 10:` Then, your program will continue.
However, if you want to compare it against the array, rather than put in a fixed number comparison, consider the following while loop:
while(myChoice > myNum.Length)
{
Console.Write("Please choose a number less than or equal to {0}: ", myNum.Length);
myChoice = Int32.Parse(Console.ReadLine());
}
This will work for any sized array then, without you having to change the while loops content. By using this system, you can then ensure that you won't get an IndexOutOfBounds exception, so long as you subtract 1 when using it as an index.
You are looking to compare a final, 11th value and trying to determine if its in an array of 10 previous entries?
Try:
for(int i = 0; i < array.length - 1; i++;)
{
If(array[i] == input)
return true;
}
return false;
You should be able to figure out how to implement this completely yourself, as you did want to do it as an exercise.
Edit: If someone wants to check this or complete it in correct syntax, go ahead. I posted this rough outline from a phone.
In general, I know that int32 errors mean that a string value is not getting converted for the console program. I have seen a lot of code trying to find the answer to this including the following stackoverflow questions (seen much more but these were most useful:
How to sum up an array of integers in C#
Error CS1501: I'm not overloading a Sum() method correctly
CS0019 Operator cannot be applied to operands of type 'bool' and 'int'
That being said, this is also a homework assignment, titled UsingSum.cs as seen in a couple of these links. The difference in mine and these is that I am trying to make it so that the user enters however many Integers they want, then they are added up. The entire assignment is written in link 2....
The problem: I keep getting either 0 or System.Int32[] instead of the sum, despite the changes I make.
I cannot use Linq.
Here is the code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace UsingSum
{
class Program
{
static void Main(string[] args)
{
int i;
int usrInput;
bool running = true;
//Enter Question Asking Loop w/ running=true
while (running)
{
Console.Write("Enter a number or enter 999 to exit: ");
int[] array1 = new int[0];
for (i = 0; i < array1.Length; i++)
{
usrInput = Convert.ToInt32(Console.ReadLine());
array1[i] = Convert.ToInt32(usrInput);
}
for (i = 0; i < array1.Length; i++)
{
Console.WriteLine(array1[i]);
}
/*If the user enters 999, calls Sum() and asks user to press any key to exit.
changes 'running' from true to false to exit the question loop*/
int exit = Convert.ToInt32 (Console.ReadLine());
if (exit == 999)
{
running = false;
Sum(array1);
}
}
//Loop complete
Console.WriteLine("Press any key to exit.");
Console.ReadLine();
}
public static void Sum(int[] numbers)
{
int [] sum1 = new int [0];
int sum2 = 0;
//Program accepts user responses with or w/o this loop...Int.32 error present both ways
//for (int a = 0; a < numbers.Length; ++a)
//sum1[a] = a;
//additional loop tried w/o the loop above/below;
//when used in the WriteLine w/ sum2 it displays 0, when used with sum1 or numbers Int.32 error
//Array.ForEach(sum1, delegate(int i) { sum2 += i; });
foreach (int i in numbers)
sum2 =+ i;
Console.WriteLine("The sum of the values in your array is: " + sum1);
/*tried changing 'numbers' to sum1, sum2, sum1.Convert.ToString(),sum2.Convert.ToString()
numbers.Convert.ToString(), also tried converting sum2 to a string.*/
}
}
}
Here is my final solution!
static void Main(string[] args)
{
AskUserForNumbers();
Console.WriteLine("Press any key to exit");
Console.ReadLine();
}
public static List<Int32> AskUserForNumbers()
{
bool running = true;
List<int> numbers = new List<int>();
while (running)
{
Console.Write("Enter a number or enter 999 to exit: ");
int inputValue;
var inputString = Console.ReadLine();
//Check for "999" which indicates we should display the numbers entered, the total and then exit our loop.
if (inputString == "999")
{
Console.WriteLine("The sum of the values in your array is: " + numbers.Sum());
running = false;
}
else if (Int32.TryParse(inputString, out inputValue) && inputValue > 0)
{
numbers.Add(inputValue);
}
else
{
Console.WriteLine("Please enter a whole number greater than 0");
}
}
return numbers;
}
}
}
A few problems:
First, you're always declaring your arrays as int[] array1 = new int[0];. This means that your code for actually getting the user input will never hit. Maybe you should try using a different collection type (List<int> maybe).
Second, you never perform any error checking when parsing the integer. That's bad practice. You should be using int.TryParse(string input, out result) to verify it was a valid number before adding it to the array.
Third, you are looping over the length of the array for inputs, meaning you will loop through however long the array is, and will continue doing so until the last input you have is the exit number (999).
Fourth, the input you get for the exit code is discarded (not added to the array to sum).
Just remember that programming is very procedural. There should be clear (logical) steps from point a to point b. In fact, imagine you are the program and you're asking a friend to give you numbers to sum up for him. Give him whatever information you think might be useful (such as the exit condition). Diagram the steps, and then try to translate that to code.
Edit: The main point is that an array (which has a fixed size) is NOT the tool for the job here. You're not actually filling the array with any data, so that's why the sum never happens. The culprit is here:
int[] array1 = new int[0]; // Instantiate a zero-length array? Can't hold any values
// Will never hit inside the loop here, because i < array1.Length (which is zero) will always be false.
for (i = 0; i < array1.Length; i++)
You need to either increase the size of the array to begin with (and either reuse the indexes or resize the array) or use an non-fixed collection (List, for example). Finally, when you pass array1 to the Sum method, array1 is empty because you declared it as a zero element array. That is why you always get a zero printing out. Like I said before, imagine you are the program, and actually run through all these steps, LINE BY LINE.
For example, you start in the loop. You prepare a miniature notebook to write down all the numbers your friend is telling you with no pages in it. For every page (and realize there are none) in the notebook, you ask your friend for a number. After you've gone through every page, you now go through every page again to read all the values he gave you (keep in mind he couldn't give you any numbers, since the notebook was empty). Then you ask him one more time for a number, and if it's 999 you tell him you're done and give him the sum of all the numbers you wrote down. If he didn't give you 999 as the number, you repeat the cycle.
Do you understand WHY it's not working now?
public static void Sum(int[] numbers)
{
int sum2 = 0;
foreach (int i in numbers)
sum2 =+ i;
Console.WriteLine("The sum of the values in your array is: " + sum2);
}
foreach (int i in numbers)
sum2 =+ i;
should become
foreach (int i in numbers)
sum2 += i;
Your problem is with your first for loop. You never will add items to your array because your
for (i = 0; i < array1.Length; i++)
Since you only add to your array1 array when you enter the loop, it won't ever increment. Since i = 0 and the array1.Length is 0 to start, i will never be less than the length.
Here is what I would suggest you do.
private static void Main(string[] args) {
var running = true;
var numbers = new List<int>();
//Enter Question Asking Loop w/ running=true
while (running) {
Console.Write("Enter a number or enter 999 to exit: ");
int inputValue;
var inputString = Console.ReadLine();
//Check for "999" which indicates we should display the numbers entered, the total and then exit our loop.
if (inputString == "999") {
//Display the numbers entered
foreach (var number in numbers) {
Console.WriteLine(number);
}
Console.WriteLine("The sum of the values in your array is: " + numbers.Sum());
running = false;
}
else if (Int32.TryParse(inputString, out inputValue) && inputValue > 0) {
//We have valid input, append it to our collection
numbers.Add(inputValue);
}
else {
//The user entered invalid data. Let them know.
Console.WriteLine("Please enter a whole number greater than 0");
}
}
//Loop complete
Console.WriteLine("Press any key to exit.");
Console.ReadLine();
}
You have several small mistakes here.
In your Sum method you are no longer using the array sum1, you're summing the values into sum2, but you're printing sum1. Your sum method should be (as described by Wiktor):
public static void Sum(int[] numbers)
{
int sum2 = 0;
foreach (int i in numbers)
sum2 += i;
Console.WriteLine("The sum of the values in your array is: " + sum2);
}
Also note that you used sum2 =+ i rather than sum2 =+ i. What that's saying is "set sum2 to be equal to the positive value of i" rather than, "add i to sum2.
Next, you have some issues in how you gather your input from the user. First off, arrays don't have a mutable size. The size that they have is fixed when they are created, and the array that you create to hold onto the values to sum up from the users is initialized to a size of 0. (int[] array1 = new int[0];) If you want to get a fixed number of values from the user you can put something other than 0 there for the array size, but based on the context it appears that you want the users to be able to add values until they enter 999 at which point you end. Since you don't know the size before hand you'll want to use a List<int> rather than an array, as you can just add items to it and it will magically grow to support the new items.
I would also suggest making a new method to get all of the values from the user, rather than embedding it in your Main method.
public static List<int> AskUserForNumbers()
{
List<int> numbers = new List<int>();
while(...)//todo determine end condition
{
string userInput = Console.ReadLine();
if(...)//todo determine if user is done
{
}
else
{
int nextNumber = ...;//todo parse user input
numbers.Add(nextNumber);
}
}
return numbers;
}
I'm not sure if it's a requirement for you to stop asking for numbers when the user enters 999 or if that's just what you did. if you have a choice, I would suggest using something different such as a blank line, 0, "quit", "exit", etc. 999 is a number that someone might want to sum.
As mentioned by SPFiredrake, it's best to use int.TryParse() to parse user input, that way if they enter a number that's not an int it won't crash, and you can tell the user that it was no good and they need to try again.