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C# returning a completely unrelated and seemingly random integer?

I am currently a complete beginner to C# however I am having this issue and as a python user the error doesn't make any sense to me. I have tried to find a fix but I don't know what to search for or how to describe the error, so please help!
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace testin
{
class Program
{
static void Main(string[] args)
{
PrintState();
CalculateAge();
EzMaths();
//Here I call the procedure which is declared later on
Console.ReadLine();
}
static void PrintState()
{
/*Here I write the procedure of 'PrintState',
* or print statement. The program will print "hey world"
* to the console as a result. */
Console.WriteLine("Hey world");
}
static void EzMaths()
{
Console.WriteLine("Enter the first number ");
Console.Write("> ");
int num1 = Console.Read();
Console.WriteLine("Enter the second number ");
Console.Write("> ");
int num2 = Console.Read();
int total = (num1 + num2);
Console.WriteLine(total);
}
static void CalculateAge()
{
Console.WriteLine("Enter your year of birth ");
Console.Write("> ");
int date = Console.Read();
int age = (2018 - date);
Console.Write("You are " + (age));
Console.ReadLine();
}
}
}

Console.Read(); does read the next Character, but as its int representation. You'll need to use Console.ReadLine();, but now you're faced with a different problem, Console.ReadLine(); returns a string and not a int, so now you need to Convert it. In the .NET World you'd do it like this:
string userInput = Console.ReadLine();
int userInputNumber = Convert.ToInt32(userInput);
This is not safe, as the user could enter something that's not a number and that would make the program crash. Of course if you're just getting started and making a "Hello World" application this is probably not your biggest concern.
I'll post the better version anyways if yo're interested:
string userInput = Console.ReadLine();
int userInputNumber;
if (int.TryParse(userInput, out userInputNumber))
{
// Do code here with userInputNumber as your number
}
And in C# (like every modern Language) we have some Syntatic Sugar to make this shorter but also harder to read:
if (int.TryParse(Console.ReadLine(), out int userInputNumber))
{
//Do code here
}

you need to use console.ReadLine() instead of console.Read() in your CalculateAge function.
refer to this answer to understand the difference between Console.Read and console.ReadLine:
Difference between Console.Read() and Console.ReadLine()?
Yet I would suggest that you also add a tryParse in order to validate if the entered value is an integer before you convert it to int
something like this:
static void CalculateAge()
{
Console.WriteLine("Enter your year of birth ");
Console.Write("> ");
string input = Console.ReadLine();
int date = 2018;
Int32.TryParse(input, out date);
int age = (2018 - date);
Console.Write("You are " + (age));
Console.ReadLine();
}
you can have another implementation if you dont want it to have a default value of 2018. like add a while loop, while tryParse != false then keep asking for input.

My code works, but I don't fully understand how

using System;
namespace SimpleweightConversion
{
public class PoundstoKilos
{
public static void Main()
{
double pounds = 0.0;
Console.Write("How many pounds? ");
double.TryParse(Console.ReadLine(), out pounds);
double kilograms = pounds * 0.453592;
Console.WriteLine("{0} pounds is equal to {1} kilograms", pounds,
kilograms);
Console.WriteLine("Press enter to exit.");
Console.ReadLine();
}
}
}
I'm trying to learn C# and I created this code to convert from pounds to kilograms, I added the tryparse bit to avoid an error if the user throws something other than numbers at the program, and it works!.The only problem I have is it doesn't clearly show when does it assign the user's input to the pounds variable, because at the start, the value of the pounds variable is 0.0, but at some point, the value provided by the user is assigned to the pounds variable, or at least that's what I think is happening.

From the Microsoft Docs, the syntax for TryParse() is:
public static bool TryParse(
string s,
out double result
)
This means that if the string s is numeric, its parsed value is immediately assigned to the variable result.
In your code, you have the line double.TryParse(Console.ReadLine(), out pounds);
In this case, the input from the console is parsed to a double, and assigned to pounds if possible.

The user's input is assigned to the pounds variable within the TryParse() method.
The out modifier indicates that the argument is being passed by reference - which means that any changes to the argument (in this case, pounds) that occur within the method call will be applied to the actual variable.

It is get assigned when u take user's input using Console. ReadLine() method.
"I.e. double.TryParse(Console.ReadLine(), out pounds);"
User's input is extracted into pounds variable.

The other answers have explained your error. I thought I'd just show you how you should write your code to make it easier to understand:
public class PoundsToKilos
{
public static void Main()
{
double pounds = 0.0;
Console.Write("How many pounds? ");
if (double.TryParse(Console.ReadLine(), out pounds))
{
//`pounds` has been assigned a value
double kilograms = pounds * 0.453592;
Console.WriteLine("{0} pounds is equal to {1} kilograms", pounds, kilograms);
}
else
{
//`pounds` has NOT been assigned a value
Console.WriteLine("You didn't enter a valid number.");
}
Console.WriteLine("Press enter to exit.");
Console.ReadLine();
}
}

C# read value from user console.read [duplicate]

What I am looking for is how to read an integer that was given by the user from the command line (console project). I primarily know C++ and have started down the C# path. I know that Console.ReadLine(); only takes a char/string. So in short I am looking for the integer version of this.
Just to give you an idea of what I'm doing exactly:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
Console.ReadLine(); // Needs to take in int rather than string or char.
I have been looking for quite a while for this. I have found a lot on C but not C#. I did find however a thread, on another site, that suggested to convert from char to int. I'm sure there has to be a more direct way than converting.

You can convert the string to integer using Convert.ToInt32() function
int intTemp = Convert.ToInt32(Console.ReadLine());

I would suggest you use TryParse:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
string input = Console.ReadLine();
int number;
Int32.TryParse(input, out number);
This way, your application does not throw an exception, if you try to parse something like "1q" or "23e", because somebody made a faulty input.
Int32.TryParse returns a boolean value, so you can use it in an if statement, to see whether or not you need to branch of your code:
int number;
if(!Int32.TryParse(input, out number))
{
//no, not able to parse, repeat, throw exception, use fallback value?
}
To your question: You will not find a solution to read an integer because ReadLine() reads the whole command line, threfor returns a string. What you can do is, try to convert this input into and int16/32/64 variable.
There are several methods for this:
Int.Parse()
Convert.ToInt()
Int.TryParse()
If you are in doubt about the input, which is to be converted, always go for the TryParse methods, no matter if you try to parse strings, int variable or what not.
Update
In C# 7.0 out variables can be declared directly where they are passed in as an argument, so the above code could be condensed into this:
if(Int32.TryParse(input, out int number))
{
/* Yes input could be parsed and we can now use number in this code block
scope */
}
else
{
/* No, input could not be parsed to an integer */
}
A complete example would look like this:
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
var foo = Console.ReadLine();
if (int.TryParse(foo, out int number1)) {
Console.WriteLine($"{number1} is a number");
}
else
{
Console.WriteLine($"{foo} is not a number");
}
Console.WriteLine($"The value of the variable {nameof(number1)} is {number1}");
Console.ReadLine();
}
}
Here you can see, that the variable number1 does get initialized even if the input is not a number and has the value 0 regardless, so it is valid even outside the declaring if block

You need to typecast the input. try using the following
int input = Convert.ToInt32(Console.ReadLine());
It will throw exception if the value is non-numeric.
Edit
I understand that the above is a quick one. I would like to improve my answer:
String input = Console.ReadLine();
int selectedOption;
if(int.TryParse(input, out selectedOption))
{
switch(selectedOption)
{
case 1:
//your code here.
break;
case 2:
//another one.
break;
//. and so on, default..
}
}
else
{
//print error indicating non-numeric input is unsupported or something more meaningful.
}

int op = 0;
string in = string.Empty;
do
{
Console.WriteLine("enter choice");
in = Console.ReadLine();
} while (!int.TryParse(in, out op));

Use this simple line:
int x = int.Parse(Console.ReadLine());

I didn't see a good and complete answer to your question, so I will show a more complete example. There are some methods posted showing how to get integer input from the user, but whenever you do this you usually also need to
validate the input
display an error message if invalid input
is given, and
loop through until a valid input is given.
This example shows how to get an integer value from the user that is equal to or greater than 1. If invalid input is given, it will catch the error, display an error message, and request the user to try again for a correct input.
static void Main(string[] args)
{
int intUserInput = 0;
bool validUserInput = false;
while (validUserInput == false)
{
try
{
Console.Write("Please enter an integer value greater than or equal to 1: ");
intUserInput = int.Parse(Console.ReadLine()); //try to parse the user input to an int variable
}
catch (Exception e) //catch exception for invalid input, such as a letter
{
Console.WriteLine(e.Message);
}
if (intUserInput >= 1) { validUserInput = true; }
else { Console.WriteLine(intUserInput + " is not a valid input, please enter an integer greater than 0."); }
} //end while
Console.WriteLine("You entered " + intUserInput);
Console.WriteLine("Press any key to exit ");
Console.ReadKey();
} //end main
In your question it looks like you wanted to use this for menu options. So if you wanted to get int input for choosing a menu option you could change the if statement to
if ( (intUserInput >= 1) && (intUserInput <= 4) )
This would work if you needed the user to pick an option of 1, 2, 3, or 4.

I used int intTemp = Convert.ToInt32(Console.ReadLine()); and it worked well, here's my example:
int balance = 10000;
int retrieve = 0;
Console.Write("Hello, write the amount you want to retrieve: ");
retrieve = Convert.ToInt32(Console.ReadLine());

Better way is to use TryParse:
Int32 _userInput;
if(Int32.TryParse (Console.Readline(), out _userInput) {// do the stuff on userInput}

Try this it will not throw exception and user can try again:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice = 0;
while (!Int32.TryParse(Console.ReadLine(), out choice))
{
Console.WriteLine("Wrong input! Enter choice number again:");
}

static void Main(string[] args)
{
Console.WriteLine("Please enter a number from 1 to 10");
int counter = Convert.ToInt32(Console.ReadLine());
//Here is your variable
Console.WriteLine("The numbers start from");
do
{
counter++;
Console.Write(counter + ", ");
} while (counter < 100);
Console.ReadKey();
}

You could create your own ReadInt function, that only allows numbers
(this function is probably not the best way to go about this, but does the job)
public static int ReadInt()
{
string allowedChars = "0123456789";
ConsoleKeyInfo read = new ConsoleKeyInfo();
List<char> outInt = new List<char>();
while(!(read.Key == ConsoleKey.Enter && outInt.Count > 0))
{
read = Console.ReadKey(true);
if (allowedChars.Contains(read.KeyChar.ToString()))
{
outInt.Add(read.KeyChar);
Console.Write(read.KeyChar.ToString());
}
if(read.Key == ConsoleKey.Backspace)
{
if(outInt.Count > 0)
{
outInt.RemoveAt(outInt.Count - 1);
Console.CursorLeft--;
Console.Write(" ");
Console.CursorLeft--;
}
}
}
Console.SetCursorPosition(0, Console.CursorTop + 1);
return int.Parse(new string(outInt.ToArray()));
}

Declare a variable that will contain the value of the user input :
Ex :
int userInput = Convert.ToInt32(Console.ReadLine());

I know this question is old, but with some newer C# features like lambda expressions, here's what I actually implemented for my project today:
private static async Task Main()
{
// -- More of my code here
Console.WriteLine("1. Add account.");
Console.WriteLine("2. View accounts.");
int choice = ReadInt("Please enter your choice: ");
// -- Code that uses the choice variable
}
// I have this as a public function in a utility class,
// but you could use it directly in Program.cs
private static int ReadInt(string prompt)
{
string? text;
do
{
Console.Write(prompt);
text = Console.ReadLine();
} while (text == null || !text.Where(c => char.IsNumber(c)).Any());
return int.Parse(new string(text.Where(c => char.IsNumber(c)).ToArray()));
}
The difference here is that if you accidentally type a number and any other text along with that number, only the number is parsed.

You could just go ahead and try :
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice=int.Parse(Console.ReadLine());
That should work for the case statement.
It works with the switch statement and doesn't throw an exception.

C# regular expressions for integers

I am trying to create a static method that validates if input is actually a number or not and I want to do it with a regex. I get an error "cannot convert int to string" when I try to do it, but it's my understanding that integers also can be compared using regex.
This is my static method so far.
public static void validatenumber(int number)
{
Regex regex = new Regex("^[0-9]+$");
if (regex.IsMatch(number))
{
Console.WriteLine("The input is a number");
}
else
{
Console.WriteLine("The input is not a number");
}
}
And this is the input that I am trying to validate, which is in the Main method.
Console.WriteLine("Please enter a number");
int number= Convert.ToInt32(Console.ReadLine());
validatenumber(number);
My variable number in my Main method needs to be an int, I cannot change that.

Your problem is not the Regex error you are getting, but the fact that you are trying to validate an int as a number. There is no sense in this validation, since the compiler will never allow an int variable to hold something else except a number.
It would make sense if yot method was receiving a string as a parameter:
validatenumber(string number)
In which case, you would not get this error, since Regex works with strings.

An issue with you code is found here, which leads to your regex (as you have to perform regex on a string not an int).
Console.WriteLine("Please enter a number");
int number= Convert.ToInt32(Console.ReadLine()); // <--- Here!
validatenumber(number);
Console.ReadLine() will return a string. So your code will throw an error or give you an unexpected result when you try to do Convert.ToInt32() on it.
You will need to change your code to look like the following:
static void Main(string[] args)
{
...
Console.WriteLine("Please enter a number");
string numberString = Console.ReadLine();
int number = ConvertAndValidateNumber(number); // we are now going to return an int
...
}
and then change the the validatenumber method to return the int type using the int.TryParse() method, which is much easier to read.
public static int ConvertAndValidateNumber(string numberString)
{
int.TryParse(numberString, out int number);
return number;
}
If you REALLY want to use RegEx (which makes sense in some very special cases), then you can change the above method to:
public static int ConvertAndValidateNumberUsingRegEx(string numberString)
{
int number;
//
// put your RegEx here...
//
// and don't forget to assign the converted string value into the number
number = (your converted string);
// return it
return number;
}
You also may want to validate that your regex is valid by testing it here http://regexr.com/

Reading an integer from user input

What I am looking for is how to read an integer that was given by the user from the command line (console project). I primarily know C++ and have started down the C# path. I know that Console.ReadLine(); only takes a char/string. So in short I am looking for the integer version of this.
Just to give you an idea of what I'm doing exactly:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
Console.ReadLine(); // Needs to take in int rather than string or char.
I have been looking for quite a while for this. I have found a lot on C but not C#. I did find however a thread, on another site, that suggested to convert from char to int. I'm sure there has to be a more direct way than converting.

You can convert the string to integer using Convert.ToInt32() function
int intTemp = Convert.ToInt32(Console.ReadLine());

I would suggest you use TryParse:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
string input = Console.ReadLine();
int number;
Int32.TryParse(input, out number);
This way, your application does not throw an exception, if you try to parse something like "1q" or "23e", because somebody made a faulty input.
Int32.TryParse returns a boolean value, so you can use it in an if statement, to see whether or not you need to branch of your code:
int number;
if(!Int32.TryParse(input, out number))
{
//no, not able to parse, repeat, throw exception, use fallback value?
}
To your question: You will not find a solution to read an integer because ReadLine() reads the whole command line, threfor returns a string. What you can do is, try to convert this input into and int16/32/64 variable.
There are several methods for this:
Int.Parse()
Convert.ToInt()
Int.TryParse()
If you are in doubt about the input, which is to be converted, always go for the TryParse methods, no matter if you try to parse strings, int variable or what not.
Update
In C# 7.0 out variables can be declared directly where they are passed in as an argument, so the above code could be condensed into this:
if(Int32.TryParse(input, out int number))
{
/* Yes input could be parsed and we can now use number in this code block
scope */
}
else
{
/* No, input could not be parsed to an integer */
}
A complete example would look like this:
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
var foo = Console.ReadLine();
if (int.TryParse(foo, out int number1)) {
Console.WriteLine($"{number1} is a number");
}
else
{
Console.WriteLine($"{foo} is not a number");
}
Console.WriteLine($"The value of the variable {nameof(number1)} is {number1}");
Console.ReadLine();
}
}
Here you can see, that the variable number1 does get initialized even if the input is not a number and has the value 0 regardless, so it is valid even outside the declaring if block

You need to typecast the input. try using the following
int input = Convert.ToInt32(Console.ReadLine());
It will throw exception if the value is non-numeric.
Edit
I understand that the above is a quick one. I would like to improve my answer:
String input = Console.ReadLine();
int selectedOption;
if(int.TryParse(input, out selectedOption))
{
switch(selectedOption)
{
case 1:
//your code here.
break;
case 2:
//another one.
break;
//. and so on, default..
}
}
else
{
//print error indicating non-numeric input is unsupported or something more meaningful.
}

int op = 0;
string in = string.Empty;
do
{
Console.WriteLine("enter choice");
in = Console.ReadLine();
} while (!int.TryParse(in, out op));

Use this simple line:
int x = int.Parse(Console.ReadLine());

I didn't see a good and complete answer to your question, so I will show a more complete example. There are some methods posted showing how to get integer input from the user, but whenever you do this you usually also need to
validate the input
display an error message if invalid input
is given, and
loop through until a valid input is given.
This example shows how to get an integer value from the user that is equal to or greater than 1. If invalid input is given, it will catch the error, display an error message, and request the user to try again for a correct input.
static void Main(string[] args)
{
int intUserInput = 0;
bool validUserInput = false;
while (validUserInput == false)
{
try
{
Console.Write("Please enter an integer value greater than or equal to 1: ");
intUserInput = int.Parse(Console.ReadLine()); //try to parse the user input to an int variable
}
catch (Exception e) //catch exception for invalid input, such as a letter
{
Console.WriteLine(e.Message);
}
if (intUserInput >= 1) { validUserInput = true; }
else { Console.WriteLine(intUserInput + " is not a valid input, please enter an integer greater than 0."); }
} //end while
Console.WriteLine("You entered " + intUserInput);
Console.WriteLine("Press any key to exit ");
Console.ReadKey();
} //end main
In your question it looks like you wanted to use this for menu options. So if you wanted to get int input for choosing a menu option you could change the if statement to
if ( (intUserInput >= 1) && (intUserInput <= 4) )
This would work if you needed the user to pick an option of 1, 2, 3, or 4.

I used int intTemp = Convert.ToInt32(Console.ReadLine()); and it worked well, here's my example:
int balance = 10000;
int retrieve = 0;
Console.Write("Hello, write the amount you want to retrieve: ");
retrieve = Convert.ToInt32(Console.ReadLine());

Better way is to use TryParse:
Int32 _userInput;
if(Int32.TryParse (Console.Readline(), out _userInput) {// do the stuff on userInput}

Try this it will not throw exception and user can try again:
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice = 0;
while (!Int32.TryParse(Console.ReadLine(), out choice))
{
Console.WriteLine("Wrong input! Enter choice number again:");
}

static void Main(string[] args)
{
Console.WriteLine("Please enter a number from 1 to 10");
int counter = Convert.ToInt32(Console.ReadLine());
//Here is your variable
Console.WriteLine("The numbers start from");
do
{
counter++;
Console.Write(counter + ", ");
} while (counter < 100);
Console.ReadKey();
}

You could create your own ReadInt function, that only allows numbers
(this function is probably not the best way to go about this, but does the job)
public static int ReadInt()
{
string allowedChars = "0123456789";
ConsoleKeyInfo read = new ConsoleKeyInfo();
List<char> outInt = new List<char>();
while(!(read.Key == ConsoleKey.Enter && outInt.Count > 0))
{
read = Console.ReadKey(true);
if (allowedChars.Contains(read.KeyChar.ToString()))
{
outInt.Add(read.KeyChar);
Console.Write(read.KeyChar.ToString());
}
if(read.Key == ConsoleKey.Backspace)
{
if(outInt.Count > 0)
{
outInt.RemoveAt(outInt.Count - 1);
Console.CursorLeft--;
Console.Write(" ");
Console.CursorLeft--;
}
}
}
Console.SetCursorPosition(0, Console.CursorTop + 1);
return int.Parse(new string(outInt.ToArray()));
}

Declare a variable that will contain the value of the user input :
Ex :
int userInput = Convert.ToInt32(Console.ReadLine());

I know this question is old, but with some newer C# features like lambda expressions, here's what I actually implemented for my project today:
private static async Task Main()
{
// -- More of my code here
Console.WriteLine("1. Add account.");
Console.WriteLine("2. View accounts.");
int choice = ReadInt("Please enter your choice: ");
// -- Code that uses the choice variable
}
// I have this as a public function in a utility class,
// but you could use it directly in Program.cs
private static int ReadInt(string prompt)
{
string? text;
do
{
Console.Write(prompt);
text = Console.ReadLine();
} while (text == null || !text.Where(c => char.IsNumber(c)).Any());
return int.Parse(new string(text.Where(c => char.IsNumber(c)).ToArray()));
}
The difference here is that if you accidentally type a number and any other text along with that number, only the number is parsed.

You could just go ahead and try :
Console.WriteLine("1. Add account.");
Console.WriteLine("Enter choice: ");
int choice=int.Parse(Console.ReadLine());
That should work for the case statement.
It works with the switch statement and doesn't throw an exception.