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C# My code is not doing math.. it is just sticking the numbers together

I am creating a friendly ai whose name is Phil ;), but I need it to be able to do math. I did try, and I also tried +=, but it wont work. For example, if I did 1+1, instead of 2, it would give me 11. Here is my code:
namespace Game
{
public static class Program
{
//commands
public static string enteredCommand;
public static string commanddomath = "doMath";
//Math command stuff
public static string MathOperation;
public static string FirstOperatorNumber;
public static string SecondOperatorNumber;
public static string FinalAwnser;
static void Main()
{
if (enteredCommand == "doMath")
{
Console.WriteLine("Ok");
Console.WriteLine("What Operation should I do?");
MathOperation = Console.ReadLine();
if (MathOperation == "+")
{
Console.WriteLine("Addition! Easy! What is the first number? ex. 6");
FirstOperatorNumber = Console.ReadLine();
Console.WriteLine("Ok, what do you want the second number to be? ex. 8");
SecondOperatorNumber = Console.ReadLine();
FinalAwnser = FirstOperatorNumber + SecondOperatorNumber;
Console.WriteLine("Ok! The awnser is..." + FinalAwnser);
}
}
else
{
Console.WriteLine("That is not a command");
}
Console.ReadKey();
}
}
}
Any help is appreciated!
Thanks

You are storing the user's input (FirstOperatorNumber and SecondOperatorNumber) as strings. The addition operator (+), when applied to two strings, performs an operation called concatenation: it adds the characters from each string to form another string.
But you want addition, which is the result of the addition operator being used on two integers. So you must store the user's input as an integer by replacing 'string' with 'int' in the variable declaration:
public static int FirstOperatorNumber;
public static int SecondOperatorNumber;
The input will still be a string, so you need to convert it as well, like this:
FirstOperatorNumber = Int32.Parse(Console.ReadLine());

I have a problem converting int to double

I'm a beginner programmer and at this moment i try to create primitive program for define variable types.
Below code and core of my problem.
namespace Moving
{
internal class Program
{
static void Main(string[] args)
{
string input = Console.ReadLine();
if (int.TryParse(input, out int result1))
{
Console.WriteLine("type int");
}
if (double.TryParse(input, out double result2))
{
Console.WriteLine("type double");
}
else
{
Console.WriteLine("type String");
}
Console.ReadLine();
}
}
}
When i use string or double it works normally. But when i input int, works first if{} and second if{} too. For example i input 12. Program writes "type int" and "type double" because int may convert to double without efforts. I don't need it. Can i don't convert variable int to double? And i haven't a clue how i can explain to program to see difference between "string" and "char". What may do with it?

Because (mathematically) 1 = 1.0 is true, knowing this we derive that all integers are also valid decimal numbers, in programming terms we call them floating point numbers, and double is a floating point number type, meaning, it represents a floating point number, and as such can also represent integers*. So technically there's no problem, but it's not behaving how we want it to behave, so how do we fix this?
Easy, we use an else if statement instead of an if statement. The else if is only checked if the if (or else if) before it is false. Implementing it looks like this:
string input = Console.ReadLine();
if (int.TryParse(input, out int intResult))
{
Console.WriteLine("Integer");
}
else if (double.TryParse(input, out double doubleResult))
{
Console.WriteLine("Double");
}
else
{
Console.WriteLine("String");
}
*Okay, so technically double (and every floating point number type) can't represent every integer perfectly, because of how they're implemented in binary, but that's a whole other topic and too advanced for now, if you ever want to know more, check out Is floating point math broken?

Well, you can try else if instead of just if. Please, note, that every int can be parsed as double and every char can be treated as string:
if (int.TryParse(input, out int result1))
Console.WriteLine("type int");
else if (double.TryParse(input, out double result2))
Console.WriteLine("type double");
else if (input.Length == 1) // char is a string of Length == 1
Console.WriteLine("type char");
else
Console.WriteLine("type String");

In your statements, there are two different condition blocks. Therefore, you will get two outputs. If you only want to get one output. You should use one condition block: If, Else If, Else.
string input = Console.ReadLine();
if (int.TryParse(input, out int result1))
{
Console.WriteLine("type int");
}
else if (double.TryParse(input, out double result2))
{
Console.WriteLine("type double");
}
else
{
Console.WriteLine("type String");
}
Console.ReadLine();

You can use Convert class to Convert int to double
int n1 = 289;
double n2;
n2 = Convert.ToDouble(n1);

Pipe sizing C# code gives unwanted result

I am new to C# and trying to figure out how to write simple codes to perform basic calculations. I tried to write code for pipe diameter and everything seems to be fine but the result is NaN.
I've tried to change locations for variables declarations as I suspect that there is a problem with. I tried also static keyword but without success.
This is the code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace Pipe_Sizing
//This simple code is intended to calculate diameter of the pipe after getting flow and velcity values from the user
{
class Program {
//This method is created to read input from users and convert it to number
static void readnum(string inp, double num) {
inp = Console.ReadLine();
while ((num = double.Parse(inp)) < 0) {
Console.WriteLine("Sorry, you need value in digits");
inp = Console.ReadLine();
}
Console.WriteLine(num);
}
static string flo;
static double flox;
static string vel;
static double velx;
static void Main()
{
// Get the Flow value from thre user
Console.WriteLine("Please Enter the value of Flow in m3/hr");
readnum(flo, flox);
// Get the Velocity value from the user
Console.WriteLine("Please Enter the value of velcoty in m/s");
readnum(vel, velx);
double dd = (4 * flox) / (3.14 * velx);
double d = Math.Sqrt(dd);
Console.WriteLine("The diameter required for the pipe is " + d);
Console.ReadLine();
}
}
}
How to get the result as a number?

The method readnum does not return anything. The parameters of readnum (inp and num) are local variables to the method - changing their values will have no effect outside the method. Therefore in the Main method the variables flox and velx will still have their default values of 0.0. Change readnum so that it returns the num it parsed from the user input.

Many big No's in your code
static void readnum(string inp, double num)
This is not doing what you think it does (I assume): double is a value Type, meaning it get passed by value and not by reference: you code is going to modify the local (to readnum method) variable. Same for string inp: even if string is a reference type, it works as a value type in this context (for more on this google string c# immutable)
When in Main you call readnum, the variable you are passing are not modified
num = double.Parse(inp)
Parse will throw an exception if the input string is not convertible to a double (same for Parse methods for int, date, etc). You may want to use TryParse and check it return value before proceeding
static double flox;
static double velx;
You actually don't need to have these variables static (nor even class member): just declare them local for the function you are using them: the bigger the scope of a variable, the harder to handle it
static string flo;
static string vel;
Same as above more or less, you actually just need a local variable within readnum
double dd = (4 * flox) / (3.14 * velx);
.Net has a very convenient Math.Pi, much better then a 3.14
This can be a cleaner (and maybe working, not tested) version of your code:
using System;
using System.Text;
public class Program
{
//This method is created to read input from users and convert it to number
static double readnum()
{
string inp = Console.ReadLine();
double res;
while (!double.TryParse(inp, out res)) // add check for negative value
{
Console.WriteLine("Sorry, you need value in digits");
inp = Console.ReadLine();
}
Console.WriteLine(res);
return res;
}
public static void Main()
{
// Get the Flow value from thre user
Console.WriteLine("Please Enter the value of Flow in m3/hr");
double flox = readnum();
// Get the Velocity value from the user
Console.WriteLine("Please Enter the value of velcoty in m/s");
double velx = readnum();
double dd = (4 * flox) / (Math.PI * velx); //
double d = Math.Sqrt(dd);
Console.WriteLine("The diameter required for the pipe is " + d);
Console.ReadLine();
}
}

How can I handle an exception in C#? [duplicate]

This question already has answers here:
Parse v. TryParse
(8 answers)
Closed 5 years ago.
I'm trying to handle an exception to avoid my program crash if double.Parse(string) tries parsing invalid values (such as strings instead of numbers). Here's what I've got:
do
{
//asking customer the amount of shirts he would like to buy any shirts they want.
numbershirtString = Console.ReadLine(); // customer types in amount of shirts they want.
numbershirts = double.Parse(numbershirtString);
keepLooping = true;
if (numbershirts < 10)
{
Console.WriteLine("You would be buying " + numbershirts + " shirts");
keepLooping = false;
}
if (numbershirts > 10)
{
Console.WriteLine("You cannot order more than 10 shirts. Please try again.");
keepLooping = true;
}
} while (keepLooping);
I would appreciate your help. Thank you in advance!

Use double.TryParse() instead. It returns true of false depending on the outcome:
double val;
bool success = double.TryParse("red", out val);
if(success)
{
// val contains a parsed value
}
else
{
// could not parse
}

To handle an exception, in C# like similar in other languages, you can use the try..catch block.
Look at the simplest syntax:
try
{
//Try to run some code.
}
catch
{
//Do something if anything excepted.
}
If you're interested to retrieve which exception breaked the code:
try
{
//Try to run some code.
}
catch (Exception ex)
{
//Do something ex was thrown.
}
If you change the type of ex to something inheriting the base class Exception you'll handle only all the exception of that type:
try
{
//Try to run some code.
}
catch (StackOverflowException ex)
{
//Do something ex was thrown because you overflowed the stack.
}
But instead of talking about try..catch block which you can find out more about on Google, I suggest you to use the method double.TryParse(string, out double).
Its syntax is a little bit different than double.Parse, but effectively it does the same in a different way.
It returns true if your input is valid, else it returns false, whereas in the first parameter you have just to pass your string input and in the second one is required an output reference to the result variable:
double x = 0;
string number = "125.3";
if (double.TryParse(number, out x))
Console.WriteLine("Your number is " + x.ToString());
else
Console.WriteLine("Your input isn't valid");

Maybe this is a little advanced for you, but if you are feeling in a clever mood, you can define a class that handles the parsing of user input. That way you can keep that logic separated from your main program (see separation of concerns).
public class UserEntry
{
private readonly string _originalValue;
public UserEntry(string input)
{
_originalValue = input;
}
public bool IsInt
{
get
{
return int.TryParse(_originalValue, out var dummy);
}
}
public int ToInt()
{
return ToInt(default(int));
}
public int ToInt(int defaultValue)
{
int result;
bool ok = int.TryParse(_originalValue, out result);
return ok ? result : defaultValue;
}
public override string ToString()
{
return _originalValue;
}
static public implicit operator UserEntry(string input)
{
return new UserEntry(input);
}
static public implicit operator Int32(UserEntry input)
{
return input.ToInt();
}
}
If we use implicit conversion operators it makes things very simple. For example, all of these are now legal:
UserEntry entry = Console.ReadLine();
if (!entry.IsInt) continue;
if (entry < 10) return entry;
If we apply this to your example, it shortens your code a bit, and arguably makes it a bit clearer as well.
public class Program
{
private const int MaximumOrder = 10;
public static void Main()
{
var n = AskForNumberOfShirts();
Console.WriteLine("OK, I'll order {0} shirts.", n);
}
public static int AskForNumberOfShirts()
{
while (true)
{
Console.WriteLine("Enter the number of shirts to order:");
UserEntry entry = Console.ReadLine();
if (!entry.IsInt)
{
Console.WriteLine("You entered an invalid number.");
continue;
}
if (entry > MaximumOrder)
{
Console.WriteLine("{0} is too many! Please enter {1} or fewer.", entry, MaximumOrder);
continue;
}
return entry;
}
}
}
Notes:
I doubt you can order half a shirt, so I am using an int instead of a double to store the number of shirts.
I refactored the logic branches to use opportunistic return, a.ka. Guard Pattern. See this article for why I do this.
I extracted the constant value 10 to its own symbol, MaximumOrder. This should get you a couple points on the assignment.
Output:
Enter the number of shirts to order:
22
22 is too many! Please enter 10 or fewer.
Enter the number of shirts to order:
sdlfkj
You entered an invalid number.
Enter the number of shirts to order:
9
OK, I'll order 9 shirts.
Working example on DotNetFiddle

How to write a function that takes an integer as a parameter and calculates and returns the squared value

Ahoy! I have just started methods but I am a tad confused when it comes to methods with math. First post so be nice :) I'm aware I out in NumberToSquare way too many times!
Write a program that asks the user to enter a number. In your program write a function called SquareValue that takes an integer parameter and calculates the square of integer parameter and returns this squared value. Your program should take this returned square value and display it. An example of the output is:
Please enter a number to square: 8
/ 8 squared is: 64
What I have so far is not so comprehensible. I thought along a few different avenues and was unsure as to what to delete. Help please.
namespace SquareValue
{
class Program
{
static void Main(string[] args)
{
int number=NumberToSquare();
SquareValue(NumberToSquare * NumberToSquare);
string output;
Console.ReadKey();
}
public int SquareValue(NumberToSquare, NumberToSquare);
{
int result = NumberToSquare * NumberToSquare;
return result;
Console.WriteLine("{0} squared is "+result");
}
public int NumberToSquare()
{
Console.WriteLine("Please enter a number to square: ");
int NumberToSquare = Console.ReadLine();
return NumberToSquare;
}
}

I see no reason to over complicate this:
public int Square(int x)
{
return (x * x);
}
or
public int Square(int x)
{
return Math.Pow(x,2);
}
Or just use Math.Pow as it exists with 2 as the Power Of number.

You seem very green on programming and I'm not sure SO is a place to go to learn the basics, but I'll run through what you've done and explain what's going wrong.
Your original program concept is fine but there are many issues with basic syntax. I understand you mightn't be familiar with reading compiler errors so I'll explain the errors that I see just reading through the code...
You put a ; at the end of the SquareValue(..., ...) method which teeminates the declaration so the body in braces isn't part of the method, then things go haywire later on.
You're not passing in the value captured from the NumberToSquare method...
int number=NumberToSquare();
SquareValue(NumberToSquare * NumberToSquare);
NumberToSquare isn't a defined variable so NumberToSquare * NumberToSquare can't calculate, what you'd want is number * number where `number is the value entered by the user.
Your definition of int SquareValue(NumberToSquare, NumberToSquare) expects two parameters although you haven't speified the type. It should be
int SquareValue(int NumberToSquare, int NumberToSquare)
but you have the same variable declared twice which is another error and then you aren't passing two parameters anyway. You want to multiply a number by itself therefore you only have a single source number so why declared two parameters? You need a single parameter method
int SquareValue(int NumberToSquare)
and call like this
int number=NumberToSquare();
SquareValue(number);
Now the SquareValue() method returns an int but you never capture it in the calling code and display the result in the method. Follow the idea in this app that the Main method will do all the orchestration and display, but the SquareValue() method should ONLY do a calculation and not any I/O. I'd also rename the NumberToSquare() method a as what is actually happening ... GetNumberToSquareFromUser().
And there's also a stray " before the closing bracket.
Console.WriteLine("{0} squared is " + result");
And you defined a string output variable which is never used.
And your methods need to be static because main(..) is a static method, not instance. If you declare a Squaring class and instantiated it then you could call non static methods from that.
Also ReadLine() returns a string which can't be assigned to an int.
And finally the result line is implicitly using String.Format behind the scenes but you haven't specified the original number for the {0} token. You could also use interpolation. You could do either of these
Console.WriteLine("{0} squared is " + result, number);
Console.WriteLine($"{number} squared is " + result);
So here's your program revised
class Program
{
static void Main(string[] args)
{
int number = GetNumberToSquareFromUser();
int result = SquareValue(number);
Console.WriteLine("{0} squared is " + result, number);
Console.ReadKey();
}
public static int SquareValue(int numberToSquare)
{
return numberToSquare * numberToSquare;
}
public static int GetNumberToSquareFromUser()
{
Console.WriteLine("Please enter a number to square: ");
int NumberToSquare = int.Parse(Console.ReadLine());
return NumberToSquare;
}
}
I hope this help, I know it's alot to take in, but I hope you take the time to read and really understand rather than just blindly submit the revised version.

When writing your methods, make them reusable. When you start using a method to output to the console in addition to its primary purpose (i.e. to square a number), its re-usability becomes minimal. It is much better to keep specific code in your main method, and put sub tasks into separate methods, such as squaring a number. Now, whenever you need to square a number, you already have a perfectly good method for that.
I didn't handle the case for users entering bad input, but that can be done in the else of the TryParse if block.
static void Main(string[] args)
{
int squredNum = 0;
int NumberToSquare = 0;
Console.WriteLine("Please enter a number to square: ");
if(int.TryParse(Console.ReadLine(), out NumberToSquare))
{
squredNum = SquareValue(NumberToSquare);
Console.WriteLine("{0} squared is {1}", NumberToSquare, squredNum);
}
Console.ReadKey();
}
static int SquareValue(int numberToSquare)
{
return numberToSquare * numberToSquare;
}
p.s. I would not recommend using Math.Pow() to square a number. No need to kill a fly with a bazooka!

Here is an example of such program with robust handling:
using System;
namespace ConsoleApp1
{
internal static class Program
{
private static void Main(string[] args)
{
while (true)
{
Console.WriteLine("Enter value to square or X to exit");
var line = Console.ReadLine();
if (line == null)
continue;
if (line.Trim().Equals("X", StringComparison.InvariantCultureIgnoreCase))
{
Console.WriteLine("Exitting ...");
break;
}
int result;
if (!int.TryParse(line, out result))
continue;
Console.WriteLine(result * result);
}
}
}
}
See the docs online, understand each statement, write your very own program then as your teacher will likely figure out you didn't pull that solely by yourself :)