Develop Reference

Making a word into a sentinel value in C#

I am currently working on a program that is a loop with a sentinel value that asks the user to enter a number or enter -99 to end the program and it runs perfectly. If I were to change that -99 to just the word "Quit" is there a certain parameter that I would have to put? For example, if I want to use a letter, I know that I could use:
char (undefined parameter) = 'A'
But how would I do this with a word? When I simply try to change the value of -99 to Quit, I receive an error as expected.
using System;
class Program {
public static void Main (string[] args) {
int sum = 0;
int counter = 0;
int max = Int32.MinValue;
int min = Int32.MaxValue;
bool keepGoing = true;
while(keepGoing) {
Console.WriteLine("Please enter a number or enter -99 to stop the program:");
int number = Convert.ToInt32(Console.ReadLine());
if (number == -99){
keepGoing = false;
} else {
counter++;
sum += number;
if (number >= max) {
max = number;
}
if (number <= min) {
min = number;
}
}
}
double average = (double) sum / counter;
Console.WriteLine($"{counter} numbers were entered.");
Console.WriteLine("The average is:" + average);
Console.WriteLine("The sum is:" + sum);
Console.WriteLine("The maximum value is:" + max);
Console.WriteLine("The minimum value is:" + min);
}
}

It's difficult to store "Quit" in an int, so the root of your problem is that you have no separation between pulling the string from the console and converting it to an int:
int number = Convert.ToInt32(Console.ReadLine());
if (number == -99){
keepGoing = false;
} else {
counter++;
If you did have a separation, it becomes possible:
string input = Console.ReadLine();
if (input == "Quit"){
keepGoing = false;
} else {
int number = Convert.ToInt32(input);
counter++;

Validating input value from console without exiting loop C#

Lets say for a console application, I want the user to enter how many dices he would like to throw. Onlu values 1-5 will be accepted. I tried doing this:
Console.WriteLine("How many dices would you like to throw?");
int amount = Convert.ToInt32(Console.ReadLine());
while(true)
{
if(amount < 1 || amount > 5)
{
Console.WriteLine("Please enter a value between 1-5");
break;
}
}
The problem here is that if the user enters an invalid number, the program stops. I want it to simply continue asking until correct value is inputed. Any ideas?
cheers.

I haven't tested it but slightly refactored your code as below, it should do what you want:
Console.WriteLine("How many dices would you like to throw?");
int amount = Convert.ToInt32(Console.ReadLine());
while(amount < 1 || amount > 5)
{
Console.WriteLine("Please enter a value between 1-5");
amount = Convert.ToInt32(Console.ReadLine());
}
EDIT: if you want to safely check whether it is an integer value, you can use the below version of code:
Console.WriteLine("How many dices would you like to throw?");
var input = Console.ReadLine();
while(!int.TryParse(input, out int amount) || amount < 1 || amount > 5)
{
Console.WriteLine("Please enter a value between 1-5");
input = Console.ReadLine();
}

You might want to check if the entered value is actually an integer.
int amount;
Console.WriteLine("How many dices would you like to throw?");
do
{
if (int.TryParse(Console.ReadLine(), out var i))
{
if (i >= 1 && i <= 5)
{
amount = i;
break;
}
Console.WriteLine("The integer value is not between 1 and 5");
}
{
Console.WriteLine("The value you entered is not an integer");
}
} while (true);
EDIT
I generally like to give the user the option to exit completely.
int amount;
Console.WriteLine("How many dices would you like to throw? Or enter 'X' to exit.");
do
{
var input = Console.ReadLine();
if(input.Equals("X", StringComparison.InvariantCultureIgnoreCase))
{
return;
}
if (int.TryParse(input, out var i))
{
if (i >= 1 && i <= 5)
{
amount = i;
break;
}
Console.WriteLine("The integer value is not between 1 and 5");
}
{
Console.WriteLine("The value you entered is not an integer");
}
} while (true);

Using correct number in calculation c#

A user enters two prime numbers which are then multiplied together, and another calculation of (a-1) * (b-1) is completed (a and b being the prime numbers entered). a function to checks the numbers entered, if the numbers are NOT prime, the user will be asked to re-enter the numbers. However, when I test this, I've noticed that if the user inputs a number which ISN'T prime, and then re-enters a prime number, the calculations are based on the number which ISN'T prime. E.g. if the user enters 2 and 4, since 4 isn't prime they are asked to enter another number, e.g 3, the calculations will be based on the numbers 2 and 4.
How can I correct this so it takes the valid prime number and not the invalid number originally entered?
namespace example
{
class Program
{
class Co_P
{
static void coprime(ref int c, int calculation)
{
if (gcd(c, calculation) == 1)
Console.WriteLine("it's Co-Prime");
else
do
{
Console.WriteLine("it isn't Co-Prime");
Console.WriteLine("Enter a Co-Prime");
c = int.Parse(Console.ReadLine());
coprime(ref c, calculation);
} while (gcd(c, calculation) != 1);
}
static int Prime_a(int a) //check a is prime
{
if (a <= 1) return 0;
for (int i = 2; i <= a / 2; i++)
{
if (a % i == 0)
{
return 0; //not prime
}
}
return 1;
}
static void result(int a) //outputs if a is prime/or not
{
if (Prime_a(a) != 0)
{
Console.WriteLine(a + " is a prime number");
}
else do
{
Console.WriteLine(a + " isn't prime number");
Console.WriteLine();
Console.WriteLine("Please make sure you enter a prime number");
a = int.Parse(Console.ReadLine());
} while (Prime_a(a) == 0);
}
static int Prime_b(int b)
{
if (b <= 1) return 0;
for (int i = 2; i <= b / 2; i++)
{
if (b % i == 0)
{
return 0;
}
}
return 1;
}
static void resultb(int b)
{
int result = Prime_b(b);
if (Prime_b(b) != 0)
{
Console.WriteLine(b + " is a prime number");
}
else do
{
Console.WriteLine(b + " is not a prime number");
Console.WriteLine("Please make sure you enter a prime number");
b = int.Parse(Console.ReadLine());
} while (Prime_b(b) == 0);
}
static void Main(string[] args)
{
int a;
Console.WriteLine("Enter a prime number for a");
a = int.Parse(Console.ReadLine());
Console.WriteLine();
result(a);
Console.WriteLine();
int b;
Console.WriteLine("Enter a prime number for b");
b = int.Parse(Console.ReadLine());
Console.WriteLine();
resultb(b);
Console.WriteLine();
int total = a * b;
Console.WriteLine("The total of the prime numbers is = " + total);
int calculation = (a - 1) * (b - 1); //calculation
Console.WriteLine();
Console.WriteLine("The result = " + calculation);
Console.WriteLine();
}
}
}

You should extend result and resultb function so it returns new prompted valid number
static int result(int a) {
var result = Prime_a(a);
if (result != 0)
...code...
return result
}
Also don't forget to reassign those values
...code...
a = result(a);
...code...
b = resultb(b);

int b;
Console.WriteLine("Enter a prime number for b");
b = int.Parse(Console.ReadLine());
Console.WriteLine();
resultb(b);
Console.WriteLine();
In line resultb(b); you are passing int to method resultb. int is a value type, or in other words, passing int to a method means passing its value to a method, where copy of that value is created. In this case a copy of b is created in method resultb. Every further change on b inside method resultb is made on copy and original stays the same.
In resultb method pass parameter by reference by adding ref keyword. Instead
static void resultb(int b)
{
// code
}
method will look like this
static void resultb(ref int b)
{
// code
}
You will call the method this way
resultb(ref b);
Here's the portion of code.
int b;
Console.WriteLine("Enter a prime number for b");
b = int.Parse(Console.ReadLine());
Console.WriteLine();
resultb(ref b);
Console.WriteLine();
Now every change on passed b inside method resultb will reflect on the original.
You should do the same for method result(int a).

How find average of numbers(by input) and also count numbers

I mean how to count and sum input numbers until receive "end".
thanks !
And also how to find out input is number or letter in c#?
class Program
{
static void Main(string[] args)
{
int n = 0;
int sum = 0;
string inp;
do
{
Console.Write("Numbers ");
inp = Console.ReadLine();
int num= Convert.ToInt16(inp);
sum = sum + num;
n++;
} while (too == "end");
int average = sum / n;
Console.WriteLine(" " + average);
Console.ReadLine();
}
}

I would suggest you use a normal while loop and also add validation to check to integer input.
For the while loop you want to loop until the input is not equal to "end":
while(inp != "end")
For the validation, you can use int.TryParse method:
int num = 0;
if (int.TryParse(inp, out num)) { }
Here is a modified example of your code:
int n = 0;
int sum = 0;
string inp = null;
while(inp != "end")
{
Console.Write("Numbers ");
inp = Console.ReadLine();
int num = 0;
if (int.TryParse(inp, out num))
{
sum = sum + num;
n++;
}
}
int average = sum / n;
Console.WriteLine(" " + average);
Console.ReadLine();

// A list to hold all of the numbers entered
List<int> numbers = new List<int>();
// Will hold the inputted string
string input;
// This needs to be outside the loop so it's written once
Console.Write("Numbers: " + Environment.NewLine);
// Keep going until we say otherwise
while (true)
{
// Get the input
input = Console.ReadLine();
// Will hold the outcome of parsing the input
int number = -1;
// Check to see if input was a valid number
bool success = int.TryParse(input, out number);
// If it was a valid number then remember it
// If ANY invalid or textual input is detected then stop
if (success)
numbers.Add(number);
else
break;
}
// Write the count and average
Console.WriteLine("Count:" + numbers.Count);
Console.WriteLine("Average:" + numbers.Average());
Console.ReadLine();
Input:
Numbers:
1
2
3
4
5
Output:
Count: 5
Average: 3
The only thing here a little different to what you specified is ANY invalid or textual entry causes it to finish, not just typing the word "end", although that obviously works too.

Calculating The Factorial of a Number

When I enter the number 6 to calculate its factorial, it returns 30 (which is wrong).
Why is my program producing incorrect output?
using System;
namespace Scenario1_2
{
class Program
{
static void Main(string[] args)
{
int counter, number, fact;
Console.WriteLine("Please enter the number you wish to factorize");
number = int.Parse(Console.ReadLine());
fact = number;
for (counter = number - 1; counter >= 1; counter--)
{
fact = fact * counter;
Console.WriteLine("The number you entered was {0} and it's factorial is {1}", number, fact);
Console.ReadLine();
}
}
}
}

You look new to programming, or least C#, so just for fun, this will blow your mind:
using System;
namespace Scenario1_2
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Please enter the number you wish to factorize");
int number = int.Parse(Console.ReadLine());
Console.WriteLine("The number you entered was {0} and it's factorial is {1}", number, Factorial(number));
Console.ReadKey(true);
}
static int Factorial(int n)
{
if (n >= 2) return n * Factorial(n - 1);
return 1;
}
}
}
No loops anywhere, and the function calls itself.
You can also do it like this:
using System;
namespace Scenario1_2
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Please enter the number you wish to factorize");
int number = int.Parse(Console.ReadLine());
Console.WriteLine("The number you entered was {0} and it's factorial is {1}", number, Factorial(number));
Console.ReadKey(true);
}
static int Factorial(int n)
{
return Enumerable.Range(1, n).Aggregate((i, r) => r * i);
}
}
}
Which is all kinds of messed up :) ...but it does get the significant work down to a single line of code.
Then there's my personal favorite, the infinite enumerable:
using System;
namespace Scenario1_2
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Please enter the number you wish to factorize");
int number = int.Parse(Console.ReadLine());
Console.WriteLine("The number you entered was {0} and it's factorial is {1}", number, Factorials().Skip(number-1).First());
Console.ReadKey(true);
}
static IEnumerable<int> Factorials()
{
int n = 1, f = 1;
while (true) yield return f = f * n++;
}
}
}

The program is paused waiting for some input. You need to move the second Console.ReadLine() out of the loop. And likely the Console.WriteLine() unless you want to see each iteration completing.

You need to move two lines out from the for loop. The modified code look like this.
using System;
namespace Scenario1_2
{
class Program
{
static void Main(string[] args)
{
int counter, number, fact;
Console.WriteLine("Please enter the number you wish to factorize");
number = int.Parse(Console.ReadLine());
fact = number;
for (counter = number - 1; counter >= 1; counter--)
{
fact = fact * counter;
}
Console.WriteLine("The number you entered was {0} and it's factorial is {1}", number, fact);
Console.ReadLine();
}
}
}
There are lots of ways to calculate Factorial. You can also do it by creating a recursive function. Google can help you a lot on these basic things.
Thanks!

int n = 4, fact = n;
for (int i = n; i > 1; i--)
{
fact *= (i - 1);
}
Console.WriteLine(fact);
Console.ReadLine();

why are You printing the message inside the loop.put it outside the loop
Console.WriteLine("The number you entered was {0} and it's factorial is {1}", number, fact);

using System;
namespace factorial
{
class Program
{
static void Main(string[] args)
{
int fact = 1;
Console.Write("Enter a number to find factorial:");
int n = int.Parse(Console.ReadLine());
for (int i = n; i > 0; i--)
{
fact = fact * i;
}
Console.Write("Factorial of" + n +"is :"+fact);
Console.ReadLine();
}
}
}

import java.util.Scanner;
public class Chapter5ProblemTwelve
{
public static void main(String [] args)
{
Scanner keyboard = new Scanner(System.in);
int number;
int factor = 1;
int counter;
System.out.print("Enter a positive integer to display the factorial number: ");
number = keyboard.nextInt();
//If the number entered is less then zero. The program will tell the user to enter a positive number
if (number <= 0)
{
System.out.println("Please enter a postive number and rerun the program again.");
}
else
{
// Math work preformed if user enters a postive number. Example if user enters 4.
// 1*1 = 1, 1*2 = 2,1*3 = 3, 1*4 = 4, The program will multiple all the answers together 1*2*3*4 = 24
for (counter = 1; counter <= number; counter++)
{
factor = factor * counter;
}
//display
System.out.println("The factorial number of " + number + " is: " + factor);
}
}
}

using System;
namespace septtwenty
{
class Program
{
static void Main(string[] args)
{
int i, number, fact;
System.Console.WriteLine("Enter the Number");
number = int.Parse(Console.ReadLine());
fact = number;
for (i = number -1; i>=1; i--)
{
fact = fact * i;
}
System.Console.WriteLine("\nFactorial of Given Number is: "+fact);
Console.ReadLine();
}
}
}