We Keep Coding

How do I correctly convert strings to ints and input them into a list?

I'm making a program that asks the user for numbers for as long as he inputs positive values.
Here's the code that I currently have written, but I've not come to complete understanding with the function of and .Parse methods.
using System;
using System.Collections.Generic;
namespace Chapter
{
class Program
{
static void Main()
{
int input;
List<int> numbers = new List<int>();
Console.WriteLine("Input number: ");
input = Convert.ToInt32(Console.ReadLine());
numbers.Add(input);
while (input >= 0)
{
Console.WriteLine("Input number: ");
input = Convert.ToInt32(Console.ReadLine());
int val = Int32.Parse(input);
numbers.Add(val);
}
Console.WriteLine("the numbers you have input are");
foreach (int number in numbers)
{
Console.Write(number + " ");
}
}
}
}

The best way to achieve this is to use the Int32.TryParse method. This allows you to validate the input and handle it accordingly as well as converting to an int.
See the below example:
using System;
using System.Collections.Generic;
public class Program
{
public static void Main()
{
int input;
List<int> numbers = new List<int>();
do
{
Console.WriteLine("Input number: ");
while (!Int32.TryParse(Console.ReadLine(), out input))
{
Console.WriteLine("The value entered was not a number, try again.");
Console.WriteLine("Input number: ");
}
if (input >= 0)
numbers.Add(input);
}
while (input >= 0);
Console.WriteLine("the numbers you have input are");
foreach (int number in numbers)
{
Console.Write(number + " ");
}
}
}

Calling Convert.ToInt32(string) or Int32.Parse(string) do nearly the same thing. The difference is that Convert.ToInt32 will return 0 if the input is null and Int32.Parse will throw an exception.
If you were to look at the implementation you will find that Convert.ToInt32 calls Int32.Parse.
Anothing thing to note is that the Convert class allows you to convert a much wider range of types to intergers. The Int32.Parse method only accepts strings.
The issue with your code is in this block:
input = Convert.ToInt32(Console.ReadLine());
int val = Int32.Parse(input);
The input value has already been converted and is now an integer. This cannot be parsed (and doesn't have to be).

When working with user input, I'd rather use int.TryParse (what if user provides "bla-bla-bla"?).
I aslo suggest using infinite loop: keep asking user until (s)he puts negative value (in which case
we break the loop):
List<int> numbers = new List<int>();
// keep reading user input
while (true) {
Console.WriteLine("Input number: ");
// We try parsing (i.e. converting) user input - Console.ReadLine()
// into integer value - number
if (!int.TryParse(Console.ReadLine(), out int number))
// if parsing fails, say, user put "aha!", we let user know it
Console.WriteLine("Not a valid integer number, please, try again");
else if (number < 0)
// if number is negative stop asking user
break;
else
// non-negative numbers are added into the list
numbers.Add(number);
}
Console.WriteLine("the numbers you have input are");
// You can print the list in one go:
Console.Write(string.Join(" ", numbers));
Parseing detail:
int.TryParse(Console.ReadLine(), out int number)
int.TryParse takes user input Console.ReadLine() as an argument and returns true or false whether parsing succeeds or not. In case parsing succeeds, number contains parsed value.

Switch jumping to default case [duplicate]

This question already has answers here:
Difference between Console.Read() and Console.ReadLine()?
(12 answers)
Closed 1 year ago.
I don't get why my integer isn't coming out correctly, Console.Read() method says it's returning an integer, why isn't WriteLine displaying it correctly?
int dimension;
dimension = Console.Read();
Console.WriteLine(""+ dimension);

Console.Read() only returns the first character of what was typed. You should be using Console.ReadLine():
Example:
int suppliedInt;
Console.WriteLine("Please enter a number greater than zero");
Int32.TryParse(Console.ReadLine(), out suppliedInt);
if (suppliedInt > 0) {
Console.WriteLine("You entered: " + suppliedInt);
}
else {
Console.WriteLine("You entered an invalid number. Press any key to exit");
}
Console.ReadLine();
Additional Resources:
MSDN - Console.Read()
MSDN - Console.ReadLine()

From the MSDN:
Return Value
Type: System.Int32 The next character from the input stream, or
negative one (-1) if there are currently no more characters to be
read.

Your program is returning but you're not seeing, would you please see below code block:
You are not be able to see the output if the output window doesn't stay.
int dimension;
dimension = Console.Read();
Console.WriteLine("" + dimension);
Console.ReadLine();

Console.Read() returns ASCII code of first symbol in input. You can do
int dimension;
dimension = Console.Read();
Console.WriteLine(""+ (char)dimension);
and you'll see right first symbol in input, as
(char)dimension
will give you symbol by it's ASCII code.

int a = 0;
if(Int32.TryParse(Console.ReadLine(), out a))
{
// Do your calculations with 'a'
}
else
{
// Some warnings
}

The Console.Read method returns only a single character wrapped in an int, so that is only applicable if you are reading a number that is only one digit long, otherwise you'll always get only the first digit.
Since the return value of Read is actually a character, you cannot use it directly as an integer, you would need to parse it from character to integer.
But assuming that you want a number that is longer than one digit, then you really need to use Console.ReadLine instead and convert the input to an integer using int.TryParse. If int.TryParse returns false you can warn the user that he provided an invalid input and ask for the dimension again.
Sample code:
int dimension;
bool isValidDimension;
do
{
Console.Write("Dimension: ");
string input = Console.ReadLine();
isValidDimension = int.TryParse(input, out dimension);
if (!isValidDimension)
{
Console.WriteLine("Invalid dimension... please try again.");
Console.WriteLine();
}
} while (!isValidDimension);

you should it as follow
static void Main()
{
int Number;
string strNumber;
strNumber = Console.ReadLine();
Number = int.Parse(strNumber);
Console.WriteLine("" + dimension);
}

How I get the right exception for wrong Datatype input?

Sorry, first of all, I´m new in C#
I´m trying to get the right way to handle the wrong input!
In my small calculator I have ints for the input and to calculate with, but I how do I handle it when I have an input like: "hi", what is not an int?
AND I want to loop if you make a wrong input again and I don´t know how to loop it....
Isn´t there anything like: if (x != int32) ?
I have tried it this way:
Console.WriteLine("Enter the first number: ");
while (!Int32.TryParse(Console.ReadLine(), out x))
{
Console.WriteLine("Invalid input! Try again");
if (Int32.TryParse(Console.ReadLine(), out x))
{
break;
}
}

You only need the following
int x;
Console.WriteLine("Enter the first number: ");
while (!Int32.TryParse(Console.ReadLine(), out x))
Console.WriteLine("Invalid input! Try again");
Console.WriteLine($"You had one job and it was a success : {x}");
Here is the deal
Console.ReadLine() returns a string, Int32.TryParse( returns true or false if it can parse a string to an int.
The loop will continually loop while Console.ReadLine() cannot be parsed to an int
As soon as it can, the loop condition is not met and execution continues to the last Console.WriteLine

How to check for a double type response in an if statement

I'm trying to check if the user's response is a double or an int, but the int is specific, whereas the double is not, as I probably made a right mess of explaining it, here's the code:
Console.WriteLine("\n 2) Q: How old is Sally? \n");
int nSallyAge = Convert.ToInt32(Console.ReadLine());
double dSallyAge = Convert.ToDouble((nSallyAge));
if (nSallyAge == 62 || dSallyAge == 62.0)
{
// Increase Score
sUser1Score++;
Console.WriteLine("\n A: Correct, Sally's age is 62, you have been awarded 1 point. \n");
Console.ReadLine();
}
What I'm trying to do, is instead of dSallyAge HAS to equal 62.0, it just has to equal any double figure.

I would approach this problem by first creating a method that gets a double from the user (that will, of course, also accept an int). This removes error handling from your main code.
NOTE in the code below, Math.Truncate can be replaced by Math.Floor, with the same result:
private static double GetDoubleFromUser(string prompt)
{
double input;
while (true)
{
if (prompt != null) Console.Write(prompt);
if (double.TryParse(Console.ReadLine(), out input)) break;
Console.WriteLine("Sorry, that is not a valid number. Please try again.");
}
return input;
}
Then, in my main code, I would get the number from the user, and use the Math.Truncate method to just read the first part of the double passed in by the user (this is what it sounds like you want to do). This means that if the user enters anything from 62 to 62.0 to 62.999, it will truncate the result to '62':
double nSallyAge = GetDoubleFromUser("2) Q: How old is Sally? ");
if (Math.Truncate(nSallyAge) == 62)
{
// Increase Score
sUser1Score++;
Console.WriteLine("A: Correct, Sally's age is 62, you have been awarded 1 point.");
Console.ReadLine();
}
Other alternative ways to use this are:
int sallyAge = Math.Truncate(GetDoubleFromUser("2) Q: How old is Sally? "));
if (sallyAge == 62)
{
// Increase Score
sUser1Score++;
Console.WriteLine("A: Correct, Sally's age is 62, you have been awarded 1 point.");
Console.ReadLine();
}
Or, you could use an input function that returns an int in the first place:
private static int GetIntFromUser(string prompt)
{
return Math.Truncate(GetDoubleFromUser(prompt));
}

In your code above, you are converting the input to an integer and then converting the int result to a double.
Assuming that you are only allowing numerical values to be entered, why not try something like this. This will identify if the input contained decimals or not:
string input = Console.ReadLine();
int iSallyAge;
double dSallyAge;
if (!Int32.TryParse(input, iSallyAge))
{
dSallyAge = Double.Parse(input);
}

You should be using Double.TryParse to parse the user input to a double and then test that value to see whether it's equal to 62.0.
double age;
if (double.TryParse(Console.ReadLine(), out age) && age == 62.0)
{
// age is 62.
// ...
}

How can I read user input from the console?

I want to get a number from the user, and then multiply that number with Pi. my attempt at this is below. But a contains gibberish. For example, if I insert 22, then a contains 50. What am I doing wrong? I don't get any compiler errors.
double a,b;
a = Console.Read();
b = a * Math.PI;
Console.WriteLine(b);

I'm not sure what your problem is (since you haven't told us), but I'm guessing at
a = Console.Read();
This will only read one character from your Console.
You can change your program to this. To make it more robust, accept more than 1 char input, and validate that the input is actually a number:
double a, b;
Console.WriteLine("istenen sayıyı sonuna .00 koyarak yaz");
if (double.TryParse(Console.ReadLine(), out a)) {
b = a * Math.PI;
Console.WriteLine("Sonuç " + b);
} else {
//user gave an illegal input. Handle it here.
}

a = double.Parse(Console.ReadLine());
Beware that if the user enters something that cannot be parsed to a double, an exception will be thrown.
Edit:
To expand on my answer, the reason it's not working for you is that you are getting an input from the user in string format, and trying to put it directly into a double. You can't do that. You have to extract the double value from the string first.
If you'd like to perform some sort of error checking, simply do this:
if ( double.TryParse(Console.ReadLine(), out a) ) {
Console.Writeline("Sonuç "+ a * Math.PI;);
}
else {
Console.WriteLine("Invalid number entered. Please enter number in format: #.#");
}
Thanks to Öyvind and abatischev for helping me refine my answer.

string input = Console.ReadLine();
double d;
if (!Double.TryParse(input, out d))
Console.WriteLine("Wrong input");
double r = d * Math.Pi;
Console.WriteLine(r);
The main reason of different input/output you're facing is that Console.Read() returns char code, not a number you typed! Learn how to use MSDN.

I think there are some compiler errors.
Writeline should be WriteLine (capital 'L')
missing semicolon at the end of a line
double a, b;
Console.WriteLine("istenen sayıyı sonuna .00 koyarak yaz");
a = double.Parse(Console.ReadLine());
b = a * Math.PI; // Missing colon!
Console.WriteLine("Sonuç " + b);

string str = Console.ReadLine(); //Reads a character from console
double a = double.Parse(str); //Converts str into the type double
double b = a * Math.PI; // Multiplies by PI
Console.WriteLine("{0}", b); // Writes the number to console
Console.Read() reads a string from console A SINGLE CHARACTER AT A TIME (but waits for an enter before going on. You normally use it in a while cycle). So if you write 25 + Enter, it will return the unicode value of 2 that is 50. If you redo a second Console.Read() it will return immediately with 53 (the unicode value of 5). A third and a fourth Console.Read() will return the end of line/carriage characters. A fifth will wait for new input.
Console.ReadLine() reads a string (so then you need to change the string to a double)

Sometime in the future .NET4.6
//for Double
double inputValues = double.Parse(Console.ReadLine());
//for Int
int inputValues = int.Parse(Console.ReadLine());

double a,b;
Console.WriteLine("istenen sayıyı sonuna .00 koyarak yaz");
try
{
a = Convert.ToDouble(Console.ReadLine());
b = a * Math.PI;
Console.WriteLine("Sonuç " + b);
}
catch (Exception)
{
Console.WriteLine("dönüştürme hatası");
throw;
}

Console.Read() takes a character and returns the ascii value of that character.So if you want to take the symbol that was entered by the user instead of its ascii value (ex:if input is 5 then symbol = 5, ascii value is 53), you have to parse it using int.parse() but it raises a compilation error because the return value of Console.Read() is already int type. So you can get the work done by using Console.ReadLine() instead of Console.Read() as follows.
int userInput = int.parse(Console.ReadLine());
here, the output of the Console.ReadLine() would be a string containing a number such as "53".By passing it to the int.Parse() we can convert it to int type.

You're missing a semicolon: double b = a * Math.PI;