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How to do while loop/Do while loop with sentinel value with switch

Hello I am trying to figure out why my program is not working, it's supposed to output a program in which department codes would be entered and followed by a prompt to enter a mark and so on until Q is entered. I can't seem to get that part working at all. If anyone could help please I will appreciate it.
// declare variables
char deptCode = ' ';
int count = 0;
double markVal, sum = 0, average = 0.0;
{
Console.WriteLine("Enter a department code: ‘C’ or ‘c’ for Computer Science,‘B’ or ‘b’ for History, ‘P’ or ‘p’ for Physics, or enter ‘Q’ or ‘q’ to quit:");
deptCode = Convert.ToChar(Console.ReadLine());
while (char.ToUpper(deptCode) != 'Q')
do
{
Console.Write("Enter a mark between 0 and 100 => ");
markVal = Convert.ToDouble(Console.ReadLine());
{
Console.WriteLine("Enter a department code: ‘C’ or ‘c’ for Computer Science,‘B’ or ‘b’ for History, ‘P’ or ‘p’ for Physics, or enter ‘Q’ or ‘q’ to quit:");
deptCode = Convert.ToChar(Console.ReadLine());
} while (markVal >= 0 && markVal <= 100);
count++;
average = (double)sum / count;
Console.WriteLine("***Error, Please Enter Valid Mark");
Console.WriteLine("The Average mark for Computer Science Students is {0}", average);
Console.WriteLine("The Average mark for Biology Students is {0}", average);
Console.WriteLine("The Average mark for Physics Students is {0}", average);
Console.ReadLine();
{

I am sympathetic to your dilemma and know it can be challenging to learn coding when you are not familiar with it. So hopefully the suggestions below may help to get you started at least down the right path. At the bottom of this is a basic “shell” but parts are missing and hopefully you will be able to fill in the missing parts.
One idea that you will find very helpful is if you break things down into pieces (methods) that will make things easier to follow and manage. In this particular case, you need to get a handle on the endless loops that you will be creating. From what I can see there would be three (3) possible endless loops that you will need to manage.
An endless loop that lets the user enter any number of discipline marks.
An endless loop when we ask the user which discipline to use
And an endless loop when we ask the user for a Mark between 0 and 100
When I say endless loop I mean that when we ask the user for a Discipline or a Mark… then, the user MUST press the “c”, “b” “p” or “q” character to exit the discipline loop. In addition the user MUST enter a valid double value between 0 and 100 to exit the Mark loop. The first endless loop will run allowing the user to enter multiple disciplines and marks and will not exit until the user presses the q character when selecting a discipline.
And finally when the user presses the ‘q’ character, then we can output the averages.
So to help… I will create two methods for you. One that will represent the endless loop for getting the Mark from the user… i.e.…. a number between 0 and 100. Then a second endless loop method that will get the Discipline from the user… i.e. … ‘c’, ‘b’, ‘p’ or ‘q’… and it may look something like…
private static char GetDisciplineFromUser() {
string userInput;
while (true) {
Console.WriteLine("Enter a department code: ‘C’ for Computer Science,‘B’ for Biology, ‘P’ for Physics, or enter ‘Q’ to quit:");
userInput = Console.ReadLine().ToLower();
if (userInput.Length > 0) {
if (userInput[0] == 'c' || userInput[0] == 'b' ||
userInput[0] == 'p' || userInput[0] == 'q') {
return userInput[0];
}
}
Console.WriteLine("Invalid discipline => " + userInput + " try again.");
}
}
Note… the loop will never end until the user selects the characters ‘c’, ‘b’, ‘p’ or ‘q’. We can guarantee that when we call the method above, ONLY those characters are returned.
Next is the endless loop to get the Mark from the user and may look something like…
private static double GetMarkFromUser() {
string userInput;
while (true) {
Console.WriteLine("Enter a mark between 0 and 100 => ");
userInput = Console.ReadLine().Trim();
if (double.TryParse(userInput, out double mark)) {
if (mark >= 0 && mark <= 100) {
return mark;
}
}
Console.WriteLine("Invalid Mark => " + userInput + " try again.");
}
}
Similar to the previous method, and one difference is we want to make sure that the user enters a valid number between 0 and 100. This is done using a TryParse method and most numeric types have a TryParse method and I highly recommend you get familiar with it when checking for valid numeric input.
These two methods should come in handy and simplify the main code. So your next issue which I will leave to you, is how are you going to store these values? When the user enters a CS 89 mark… how are you going to store this info? In this simple case… six variables may work like…
int totalsCSMarks = 0;
int totalsBiologyMarks = 0;
int totalsPhysicsMarks = 0;
double totalOfAllCSMarks = 0;
double totalOfAllBiologyMarks = 0;
double totalOfAllPhysicsMarks = 0;
Now you have something to store the users input in.
And finally the shell that would work using the methods above and you should see this uncomplicates things a bit in comparison to your current code. Hopefully you should be able to fill in the missing parts. Good Luck.
static void Main(string[] args) {
// you will need some kind of storage for each discipline.. see above...
char currentDiscipline = 'x';
double currentMark;
while (currentDiscipline != 'q') {
currentDiscipline = GetDisciplineFromUser();
if (currentDiscipline != 'q') {
currentMark = GetMarkFromUser();
switch (currentDiscipline) {
case 'c':
// add 1 to total number of CS marks
// add currentMarkValue to the total of CS marks
break;
case 'b':
// add 1 to total number of Biology marks
// add currentMarkValue to the total of Biology marks
break;
default: // <- we know for sure that only p could be left
// add 1 to total number of Physics marks
// add currentMarkValue to the total of Physics marks
break;
}
}
}
Console.WriteLine("Averages ------");
//Console.WriteLine("The Average mark for Computer Science Students is {0}", totalOfAllCSMarks / totalCSMarks);
//Console.WriteLine("The Average mark for Biology Students is {0}", ...);
//Console.WriteLine("The Average mark for Physics Students is {0}", ...);
Console.ReadLine();
}

How to use same variable for string input in one case, and int input in another case? (C#)

Quick question how do I use same variable for string input in case and int input in another case. Here is what I mean by that, I have a problem where I need to constantly insert number and then put the addition of those numbers inside another variable. This inserting is inside do while loop, for me to exit the loop and to show the sum of those numbers, I need to type "OK" or "ok". I have a problem where I do not know how to use string variable for int inputs.
Here is my code:
string input= "";
int sum = 0;
do
{
Console.WriteLine("Insert the number or OK (ok) for exit: ");
input = Console.ReadLine();
sum += Convert.ToInt32(input);
// this is where I get the error Input string was not in the correct fromat
} while (input != "OK" && input != "ok");
Console.WriteLine(sum)
If anyone knows how to help me with this, I would gladly appreciate it.

First identify that the user entered integer or not using int.TryParse(), if user entered integer then add it to the sum variable otherwise check the string
do
{
Console.WriteLine("Insert the number or OK (ok) for exit: ");
input = Console.ReadLine();
//This will add number only if user enters integer.
if(int.TryParse(input, out int number)
sum += number
} while (input != "OK" && input != "ok");

You have to test for OK before you try to convert to a number, because OK won't convert to a number
string input= "";
int sum = 0;
while(true)
{
Console.WriteLine("Insert the number or OK (ok) for exit: ");
input = Console.ReadLine();
if("OK".Equals(input, StringComparison.OrdinalIgnoreCase)) //do a case insensitive check. Note that it's acceptable to call methods on constants, and doing a string check this way round cannot throw a NullReferenceException
break;//exit the loop
sum += Convert.ToInt32(input);
}
Console.WriteLine(sum);
You'll still get the error if the user enters input other than OK, that is not convertible to a number, but this is the crux of your current problem. I'll leave dealing with other garbages as an exercise for you...

Code won't give desired output or read second input

Sorry if this isn't the right. This is my first time posting here. I'm a first year Software student and for the life of me i cannot seem to get this to work. I know its something simple I'm missing but oh well. I tried doing this using methods but again no help. Maybe you guys could help me?
The problem is the code wont let me input after the "Are you a member (Y/N)" writline statement and just keeps giving me an output of 50.
static void Main(string[] args)
{
//Local Variable Declaration//
double rate1 = 10;
double rate2 = 3;
double maxCharge = 50;
double charge;
Console.WriteLine("Enter number of hours (-999 to quit) : ");
int hoursRented = Console.Read();
if (hoursRented >= 3)
{
charge = hoursRented * rate1;
}
else
{
charge = (3 * rate1) + (hoursRented * rate2);
}
if (charge > maxCharge)
{
charge = maxCharge;
}
Console.WriteLine("Are you a member? (Y/N) : ");
int memberStatus = Console.Read();
if (memberStatus.Equals("Y"))
{
charge = (charge * 1 / 10) - charge;
}
Console.WriteLine("Customer Charge : {0} Total Charge To Date : ", charge);
}

The problematic lines are below
Console.WriteLine("Enter number of hours (-999 to quit) : ");
int hoursRented = Console.Read();
if (hoursRented >= 3) {
and
Console.WriteLine("Are you a member? (Y/N) : ");
int memberStatus = Console.Read();
if (memberStatus.Equals("Y")) {
When you call Console.Read(), it reads only characters and returns it as an int. You seem to mistakenly think it will parse the character to an int.
Secondly, think what happens when you provide multiple characters as input to a single Console.Read() call. Interestingly, the remaining characters are read in the subsequent calls. So when you type any number followed by Enter in the first Console.Read it only, reads the first character, the subsequent characters, including the EOLN char are returned in the subsequent calls, instead of prompting you to enter information for the next call.
The fix is easy. Use Console.Readline() and int.parse (or its int.TryParse() variant
Then the corresponding code will look like below
Console.Write("Enter number of hours (-999 to quit) : ");
string hoursRentedStr = Console.ReadLine();
int hoursRented = int.Parse(hoursRentedStr);
if (hoursRented >= 3) {
and
Console.Write("Are you a member? (Y/N) : ");
string memberStatus = Console.ReadLine();
if (memberStatus.Equals("Y")) {

This is because you are just writing:
Console.WriteLine("Are you a member? (Y/N) : ");
and continuing through.
you must do it like this:
Console.WriteLine("Are you a member? (Y/N) : ");
Console.ReadLine();
and then:
int memberStatus = Int.Parse(Console.ReadKey());

your problem is that your are using Console.Read wich returns the ascii code of the next charachter as said by #juharr in the comments. so the solution is too simply replace Read By ReadLine and change your code like this, so that ReadLine wich is a string will be converted to the int value that you want
int hoursRented = int.Parse(Console.ReadLine());
And change your member status to a string to compare it with "Y" easily
string memberStatus = Console.ReadLine();
Note: if you want to validate the input you should use a int.TryParse instead of just a normal parse like I used as it returns a bool so you knows when it fails

Converting keyboard input numbers into a numeric type

I m a bit stuck here. Though I know how to convert keyboard input character into usable character in C#.
char ch = (char)console.read();
I want to read numbers nd make them behave as numbers in my program.
If I enter 5 from keyboard I want to store as 5 (mathematical) not character 5.

I think you want something like this:
int Number;
string strNumber;
strNumber = Console.ReadLine();
Number = int.Parse(strNumber);

int i = ch - '0'; ////.........

Safest way would be something like;
int Num = 0;
if( int.TryParse( ch.ToString(), out Num ) )
{
// Num is now set correctly
}
else
{
// ch didn't contain a digit.
}

Try Convert.ToInt32("5"), a safe alternative is Int32.TryParse() here are the docs:
http://msdn.microsoft.com/en-us/library/system.convert_methods
http://msdn.microsoft.com/en-us/library/system.int32.tryparse.aspx

string a = Console.ReadLine();
int b = int.Parse(a);
Console.WriteLine(b*b);

How to Fill an array from user input C#?

What would be the best way to fill an array from user input?
Would a solution be showing a prompt message and then get the values from from the user?

string []answer = new string[10];
for(int i = 0;i<answer.length;i++)
{
answer[i]= Console.ReadLine();
}

Could you clarify the question a bit? Are you trying to get a fixed number of answers from the user? What data type do you expect -- text, integers, floating-point decimal numbers? That makes a big difference.
If you wanted, for instance, an array of integers, you could ask the user to enter them separated by spaces or commas, then use
string foo = Console.ReadLine();
string[] tokens = foo.Split(",");
List<int> nums = new List<int>();
int oneNum;
foreach(string s in tokens)
{
if(Int32.TryParse(s, out oneNum))
nums.Add(oneNum);
}
Of course, you don't necessarily have to go the extra step of converting to ints, but I thought it might help to show how you would.

It made a lot more sense to add this as an answer to arin's code than to keep doing it in comments...
1) Consider using decimal instead of double. It's more likely to give the answer the user expects. See http://pobox.com/~skeet/csharp/floatingpoint.html and http://pobox.com/~skeet/csharp/decimal.html for reasons why. Basically decimal works a lot closer to how humans think about numbers than double does. Double works more like how computers "naturally" think about numbers, which is why it's faster - but that's not relevant here.
2) For user input, it's usually worth using a method which doesn't throw an exception on bad input - e.g. decimal.TryParse and int.TryParse. These return a Boolean value to say whether or not the parse succeeded, and use an out parameter to give the result. If you haven't started learning about out parameters yet, it might be worth ignoring this point for the moment.
3) It's only a little point, but I think it's wise to have braces round all "for"/"if" (etc) bodies, so I'd change this:
for (int counter = 0; counter < 6; counter++)
Console.WriteLine("{0,5}{1,8}", counter, array[counter]);
to this:
for (int counter = 0; counter < 6; counter++)
{
Console.WriteLine("{0,5}{1,8}", counter, array[counter]);
}
It makes the block clearer, and means you don't accidentally write:
for (int counter = 0; counter < 6; counter++)
Console.WriteLine("{0,5}{1,8}", counter, array[counter]);
Console.WriteLine("----"); // This isn't part of the for loop!
4) Your switch statement doesn't have a default case - so if the user types anything other than "yes" or "no" it will just ignore them and quit. You might want to have something like:
bool keepGoing = true;
while (keepGoing)
{
switch (answer)
{
case "yes":
Console.WriteLine("===============================================");
Console.WriteLine("please enter the array index you wish to get the value of it");
int index = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("===============================================");
Console.WriteLine("The Value of the selected index is:");
Console.WriteLine(array[index]);
keepGoing = false;
break;
case "no":
Console.WriteLine("===============================================");
Console.WriteLine("HAVE A NICE DAY SIR");
keepGoing = false;
break;
default:
Console.WriteLine("Sorry, I didn't understand that. Please enter yes or no");
break;
}
}
5) When you've started learning about LINQ, you might want to come back to this and replace your for loop which sums the input as just:
// Or decimal, of course, if you've made the earlier selected change
double sum = input.Sum();
Again, this is fairly advanced - don't worry about it for now!

C# does not have a message box that will gather input, but you can use the Visual Basic input box instead.
If you add a reference to "Microsoft Visual Basic .NET Runtime" and then insert:
using Microsoft.VisualBasic;
You can do the following:
List<string> responses = new List<string>();
string response = "";
while(!(response = Interaction.InputBox("Please enter your information",
"Window Title",
"Default Text",
xPosition,
yPosition)).equals(""))
{
responses.Add(response);
}
responses.ToArray();

Try:
array[i] = Convert.ToDouble(Console.Readline());
You might also want to use double.TryParse() to make sure that the user didn't enter bogus text and handle that somehow.

I've done it finaly check it and if there is a better way tell me guys
static void Main()
{
double[] array = new double[6];
Console.WriteLine("Please Sir Enter 6 Floating numbers");
for (int i = 0; i < 6; i++)
{
array[i] = Convert.ToDouble(Console.ReadLine());
}
double sum = 0;
foreach (double d in array)
{
sum += d;
}
double average = sum / 6;
Console.WriteLine("===============================================");
Console.WriteLine("The Values you've entered are");
Console.WriteLine("{0}{1,8}", "index", "value");
for (int counter = 0; counter < 6; counter++)
Console.WriteLine("{0,5}{1,8}", counter, array[counter]);
Console.WriteLine("===============================================");
Console.WriteLine("The average is ;");
Console.WriteLine(average);
Console.WriteLine("===============================================");
Console.WriteLine("would you like to search for a certain elemnt ? (enter yes or no)");
string answer = Console.ReadLine();
switch (answer)
{
case "yes":
Console.WriteLine("===============================================");
Console.WriteLine("please enter the array index you wish to get the value of it");
int index = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("===============================================");
Console.WriteLine("The Value of the selected index is:");
Console.WriteLine(array[index]);
break;
case "no":
Console.WriteLine("===============================================");
Console.WriteLine("HAVE A NICE DAY SIR");
break;
}
}

Add the input values to a List and when you are done use List.ToArray() to get an array with the values.

of course....Console.ReadLine always return string....so you have to convert type string to double
array[i]=double.Parse(Console.ReadLine());

readline is for string..
just use read