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Local variables - switch case

I am studying programming and I am very beginner (started 2 months ago).
I am doing a c# exercise for maths calculation. Our professor used a if ... else (embricated) loops to do the exercise. I wanted to use a switch case but I am struggling with the local variables.
I understand the issue: case 2 and 3 does not "know" the variables totalNumber and nbrSubAssy is as they come from case 1 and case 2, then they are detected as not assigned.
If I still want to use a switch case, what could I do to solve it?
using System;
namespace Denombrements
{
class Program
{
static long IntMultiplication(int startValue, int endValue)
{
long multiplication = 1;
for (int k = startValue; k <= endValue; k++)
multiplication *= k;
return multiplication;
}
static int UserSelection(String message)
{
int number = 0;
Console.Write(message);
try
{
number = int.Parse(Console.ReadLine());
Console.WriteLine();
}
catch
{
Console.WriteLine();
Console.WriteLine("Wrong input, enter an integer");
}
return number;
}
static void Main(string[] args)
{
char choice = '1';
while (choice != '0')
{
Console.WriteLine("Permutation ...................... 1");
Console.WriteLine("Arrangement ...................... 2");
Console.WriteLine("Combination ...................... 3");
Console.WriteLine("Quit ............................. 0");
Console.Write("Choice : ");
choice = Console.ReadKey().KeyChar;
Console.WriteLine();
switch(choice)
{
case '0':
Environment.Exit(0);
break;
case '1':
int totalNumber = UserSelection("Total number of elements to be taken into account");
long permutation = IntMultiplication(1, totalNumber);
Console.WriteLine(totalNumber + "! = " + permutation);
break;
case '2':
int nbrSubAssy = UserSelection("Total number of elements in the subassy to be taken into account");
long arrangement = IntMultiplication(totalNumber - nbrSubAssy + 1, totalNumber);
Console.WriteLine("A(" + totalNumber + "/" + nbrSubAssy + ") = " + arrangement);
break;
case '3':
long combination = arrangement / IntMultiplication(1, nbrSubAssy);
Console.WriteLine("C(" + totalNumber + "/" + nbrSubAssy + ") = " + combination);
break;
default:
Console.WriteLine("Wrong input");
break;
}
}
Console.ReadLine();
}
}
}

Declare your variable before While loop and it will keep the value of it for all the life of LOOP and you could access the old values
char choice = '1';
int nbrSubAssy = 0;
int totalNumber = 0;
long arrangement = 0;
while (choice != '0')
{
// code ...
switch (choice)
{
case '0':
Environment.Exit(0);
break;
case '1':
totalNumber = UserSelection("Total number of elements to be taken into account");
long permutation = IntMultiplication(1, totalNumber);
Console.WriteLine(totalNumber + "! = " + permutation);
break;
case '2':
nbrSubAssy = UserSelection("Total number of elements in the subassy to be taken into account");
arrangement = IntMultiplication(totalNumber - nbrSubAssy + 1, totalNumber);
Console.WriteLine("A(" + totalNumber + "/" + nbrSubAssy + ") = " + arrangement);
break;
case '3':
long combination = arrangement / IntMultiplication(1, nbrSubAssy);
Console.WriteLine("C(" + totalNumber + "/" + nbrSubAssy + ") = " + combination);
break;
default:
Console.WriteLine("Wrong input");
break;
}
}
or in my opinion the better solution you could ask for the value in every case you need them

Running this calculator in loop in console

I am trying to make this console calculator running in loop until the user want to exit the application. How can i use a for loop with if else statements, is it possible?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Oppgave3Lesson1
{
class Program
{
static void Main(string[] args)
{
double sum = 0;
double num1;
Console.WriteLine("First number: ");
num1 = Convert.ToInt32(Console.ReadLine());
double num2;
Console.WriteLine("Second number: ");
num2 = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Addisjon eller Subtraksjon?");
string regneoperasjon = Console.ReadLine();
if(regneoperasjon == "Subtraksjon")
{
Console.WriteLine("Svaret til denne regneoperasjonen er: " + (sum = num1 - num2));
}
else if (regneoperasjon == "Addisjon")
{
Console.WriteLine("Svaret til denne regneoperasjonen er: " + (sum = num1 + num2));
}
Console.WriteLine("Do you want to do an another math operation?");
Console.ReadLine();
}
}
}

You can add a question for user via Console.ReadKey method and then check his answer:
do
{
double sum = 0;
double num1;
Console.WriteLine("First number: ");
num1 = Convert.ToInt32(Console.ReadLine());
double num2;
Console.WriteLine("Second number: ");
num2 = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Addisjon eller Subtraksjon?");
string regneoperasjon = Console.ReadLine();
if(regneoperasjon == "Subtraksjon")
{
Console.WriteLine("Svaret til denne regneoperasjonen er: " + (sum = num1 - num2));
}
else if (regneoperasjon == "Addisjon")
{
Console.WriteLine("Svaret til denne regneoperasjonen er: " + (sum = num1 + num2));
}
Console.WriteLine("Calculate the next operation (Y/N)?");
}
while(Console.ReadKey(true).Key == ConsoleKey.Y);
So you get the output like in the screenshot below:

Try following. I made the writlines a write :
namespace Oppgave3Lesson1
{
class Program
{
static void Main(string[] args)
{
while(true)
{
double sum = 0;
double num1;
Console.Write("First number: (or Exit)");
string firstNumStr = Console.ReadLine();
if(firstNumStr == "Exit") break;
num1 = Convert.ToInt32(firstNumStr);
double num2;
Console.Write("Second number: ");
num2 = Convert.ToInt32(Console.ReadLine());
Console.Write("Addisjon eller Subtraksjon?");
string regneoperasjon = Console.ReadLine();
if(regneoperasjon == "Subtraksjon")
{
Console.Write("Svaret til denne regneoperasjonen er: " + (sum = num1 - num2));
}
else if (regneoperasjon == "Addisjon")
{
Console.Write("Svaret til denne regneoperasjonen er: " + (sum = num1 + num2));
}
}

A for loop is used when you know the (maximum) number of iterations upfront.
In your scenario, a while loop is more apropriate.
do
{
// Perform your logic here
Console.WriteLine("Press any key to continue; Q to quit");
var key = Console.ReadKey();
}while( key != ConsoleKey.Q );
or, use an endless while - loop and break from the loop on a certain condition:
while( true )
{
// Perform your logic here
Console.WriteLine("Press any key to continue; Q to quit");
var key = Console.ReadKey();
if( key == ConsoleKey.Q )
{
break;
}
}

c# (beginner) how to make a short version of this "if" code? [closed]

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I just learned how to use if and tried to do a simple calculator. but the code is way too long and i want to add more options to it, can i make it any shorter using any other method?
namespace ConsoleApp4
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("How many numbers do you wish to calculate? ");
string HowMany = Console.ReadLine();
if (HowMany == "2") {
Console.Write("Enter #1: ");
int x = int.Parse(Console.ReadLine());
Console.Write("Enter #2: ");
int y = int.Parse(Console.ReadLine());
int sum = x + y; int sub = x - y; int mult = x * y; int div = x / y;
Console.WriteLine("The Result : Sum = " + sum + " Sub = " + sub + " Mult = " + mult + " Div = " + div); }
else if (HowMany == "3") {
Console.Write("Enter #1: ");
int x = int.Parse(Console.ReadLine());
Console.Write("Enter #2: ");
int y = int.Parse(Console.ReadLine());
Console.Write("Enter #3: ");
int z = int.Parse(Console.ReadLine());
int sum = x + y + z; int sub = x - y - z; int mult = x * y * z; int div = x / y / z;
Console.WriteLine("The Result : Sum = " + sum + " Sub = " + sub + " Mult = " + mult + " Div = " + div); }
else if (HowMany == "4")
{
Console.Write("Enter #1: ");
int x = int.Parse(Console.ReadLine());
Console.Write("Enter #2: ");
int y = int.Parse(Console.ReadLine());
Console.Write("Enter #3: ");
int z = int.Parse(Console.ReadLine());
Console.Write("Enter #4: ");
int w = int.Parse(Console.ReadLine());
int sum = x + y + z + w; int sub = x - y - z - w; int mult = x * y * z * w; int div = x / y / z / w;
Console.WriteLine("The Result : Sum = " + sum + " Sub = " + sub + " Mult = " + mult + " Div = " + div);
}
Console.ReadKey();
}
}
}

This does just the sum. I'll leave handling the other calculations to you.
int sum = 0;
for(int i = 1;i<=HowMany;i++)
{
Console.Write("Enter #{0}: ", i);
int input = int.Parse(Console.ReadLine());
sum += input;
}
Console.WriteLine("The Result : Sum = {0}", sum);

using System.IO;
using System;
class Program {
static void Main() {
Console.WriteLine("How many numbers do you wish to calculate? ");
string HowMany = Console.ReadLine();
int[] nums = new int[int.Parse(HowMany)];
int sum = 0, sub = 0, mult = 1, div = 1;
for (int i = 0; i < int.Parse(HowMany); i++) {
Console.Write("Enter #" + (i + 1) + ": ");
nums[i] = int.Parse(Console.ReadLine());
sum += nums[i];
sub -= nums[i];
mult *= nums[i];
div /= nums[i];
}
Console.WriteLine("The Result : Sum = " + sum + " Sub = " + sub + " Mult = " + mult + " Div = " + div);
Console.ReadKey();
}
}

You can just use a loop, and keep a rolling total of the values. Also, I changed div to be a double, because integer division is really boring - it's nice to see the decimal value:
I also made it so the user can only enter an integer greater than zero for the quantity of numbers they want to calculate.
And finally, they can only enter a non-zero integer for the number, because a zero input means we have to do some check for that during division, the multiplication value will always be zero, and it does nothing to the addition and subtraction totals.
Console.Write("How many numbers do you wish to calculate? ");
int count;
while (!int.TryParse(Console.ReadLine(), out count) || count < 1)
{
Console.Write("Error: enter a positive, whole number: ");
}
int input, sum = 0, sub = 0, mult = 0;
double div = 0;
for (int i = 1; i <= count; i++)
{
Console.Write($"Enter #{i}: ");
// Don't allow user to enter 0. It does nothing to the addition or subtraction
// values, will make the multiplication value zero, and cannot be use for division
while (!int.TryParse(Console.ReadLine(), out input) || input == 0)
{
Console.Write("Error: enter a non-zero whole number: ");
}
if (i == 1)
{
// On the first input, we just store the number
sum = sub = mult = input;
div = input;
}
else
{
sum += input;
sub -= input;
mult *= input;
div /= input;
}
}
Console.WriteLine("The Result : Sum = " + sum + " Sub = " +
sub + " Mult = " + mult + " Div = " + div);
Console.ReadKey();

C# variable changes value unexpectedly

The title basically says it all. The variable "answer" in my code randomly changes value to another random number when it is defined.
The program is supposed to ask ten random maths questions and tell the user if they have got the correct answer or not, however this doesn't seem to be working at all.
Once the variable has changed, the program then also asks about 3 more questions, and tells the user the answer to each is incorrect.
static void Main(string[] args)
{
Random R = new Random();
double solution = 0;
string sign = "";
int score = 0;
for (int i = 0; i < 10; i++)
{
int X = R.Next(1, 5);
int Y = R.Next(1,10);
int Z = R.Next(1,10);
switch (X)
{
case 1:
solution = Y + Z;
sign = "+";
break;
case 2:
solution = Y - Z;
sign = "-";
break;
case 3:
solution = Y / Z;
sign = "/";
break;
case 4:
solution = Y * Z;
sign = "X";
break;
}
Console.WriteLine("What is " + Y + " " + sign + " " + Z + "?");
double answer = Console.Read();
if (answer == solution)
{
Console.WriteLine("Correct");
score = score + 1;
Console.Read();
}
else if (answer != solution)
{
Console.WriteLine("Incorrect. The correct answer is " + solution);
Console.Read();
}
else
{
Console.WriteLine("Error");
Console.Read();
}
}
}
}
}

Your problem is in Console.Read(). This will return the characters number. Starting at 48 (0x30) for character 0. That's why all of your answers are incorrect.
So I suggest you use Console.ReadLine() and then parse the string to answer.
double answer;
if (!double.TryParse(Console.ReadLine(), out answer))
{
Console.WriteLine("Error");
continue;
}
if (answer == solution)
{
Console.WriteLine("Correct");
score = score + 1;
}
else if (answer != solution)
{
Console.WriteLine("Incorrect. The correct answer is " + solution);
}

The problem is that you are using Console.Read() which returns only the next character code. Instead, you should use Console.ReadLine(). Also after you check the answers you use some unnecessary Console.Read()(s). I have removed them and this code is working perfectly fine: -
static void Main(string[] args)
{
Random R = new Random();
double solution = 0;
string sign = "";
int score = 0;
for (int i = 0; i < 10; i++)
{
int X = R.Next(1, 5);
int Y = R.Next(1,10);
int Z = R.Next(1,10);
switch (X)
{
case 1:
solution = Y + Z;
sign = "+";
break;
case 2:
solution = Y - Z;
sign = "-";
break;
case 3:
solution = Y / Z;
sign = "/";
break;
case 4:
solution = Y * Z;
sign = "X";
break;
}
Console.WriteLine("What is " + Y + " " + sign + " " + Z + "?");
double answer = double.Parse(Console.ReadLine());
if (answer == solution)
{
Console.WriteLine("Correct");
score = score + 1;
}
else if (answer != solution)
{
Console.WriteLine("Incorrect. The correct answer is " + solution);
}
}
}
Another thing is that the division questions are actually integer divisions. If you want decimals instead, you should use something like solution = Math.Round((double)((decimal)Y / (decimal)Z), 3); to check a value rounded to 3 decimal places.

I think your problem lies in the fact that Console.Read returns an integer code for the last character pressed (see https://msdn.microsoft.com/en-us/library/system.console.read(v=vs.110).aspx for details).
You need code something like this:
double answer = double.Parse(Console.ReadLine());
This takes the entire input (which might be more than one character) and converts it to a double (Console.ReadLine returns a string) so you are comparing like with like.

Console.Read();
returns an int value(The ASCII code) and you are storing this as answer which is of type double ! Use
Console.ReadLine();
instead ! Also you need to convert your answer to a double value to be able to compare your answer to the solution!

C# Console Output Formatting

I'm trying to get a factorial to be displayed as for example (factorial of 5 is 5*4*3*2*1)
I'm using a method for the factorial, but it doesn't accept the line Console.Write(i + " x "); in my code.
Any help would be great.
here is my code.
//this method asks the user to enter a number and returns the factorial of that number
static double Factorial()
{
string number_str;
double factorial = 1;
Console.WriteLine("Please enter number");
number_str = Console.ReadLine();
int num = Convert.ToInt32(number_str);
// If statement is used so when the user inputs 0, INVALID is outputed
if (num <= 0)
{
Console.WriteLine("You have entered an invalid option");
Console.WriteLine("Please enter a number");
number_str = Console.ReadLine();
num = Convert.ToInt32(number_str);
//Console.Clear();
//topmenu();
//number_str = Console.ReadLine();
}
if (num >= 0)
{
while (num != 0)
{
for (int i = num; i >= 1; i--)
{
factorial = factorial * i;
}
Console.Write(i + " x ");
Console.Clear();
Console.WriteLine("factorial of " + number_str.ToString() + " is " + factorial);
factorial = 1;
Console.WriteLine("(please any key to return to main menu)");
Console.ReadKey();
Console.Clear();
topmenu();
}
}
return factorial;
}
Thank you!

The problem is that your for loop isn't using braces, so the scope is just one line.
Try adding braces appropriately:
for (int i = num; i >= 1; i--)
{
factorial = factorial * i;
Console.Write(i.ToString() + " x ");
}
Console.WriteLine("factorial of " + number_str.ToString() + " is " + factorial);
Without the braces, the i variable only exists on the next statement (factorial = factorial * i;), and no longer exists in scope by the time you call Console.Write.
You will likely also want to remove the call to Console.Clear immediately following this Write, or you will not see it.

here's a solution to consider
public static void Main()
{
Console.WriteLine("Please enter number");
int input;
while (!int.TryParse(Console.ReadLine(), out input) || input <= 0)
{
Console.WriteLine("You have enter an invald option");
Console.WriteLine("Please enter number");
}
Console.Write("Factorial of " + input + " is : ");
int output = 1;
for (int i = input; i > 0; i--)
{
Console.Write((i == input) ? i.ToString() : "*" + i);
output *= i;
}
Console.Write(" = " +output);
Console.ReadLine();
}
int.TryParse() will be beneficial for you, so the program doesn't crash if the user inputs a non-integer
also, you may want something besides an integer. Factorials get very large very fast - anything over 16 will return a wrong result.