Develop Reference

How to change the sign to a decimal number in C#

I need a console app that changes the sign to a certain typed number. You type 10, it gives you -10. And so on. I've managed to do that, but I can't do it if I type 1.5 for example. Or any decimal number.
I get "Input string was not in a correct format".
this is what I did.
string inputData = Console.ReadLine();
int a = Convert.ToInt32 (inputData);
int b = a * (-1);
Console.WriteLine(b);
Console.ReadLine();

You need to use decimal as a variable type if you want to work with decimal numbers
If so, use Convert.ToDecimal instead of ToInt32
You don't really need to use multiplication here, it's enough just to use -a instead
string inputData = Console.ReadLine();
decimal a = Convert.ToDecimal (inputData);
decimal b = -a;
Console.WriteLine(b);
Console.ReadLine();

3 equals 51 in C# [duplicate]

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;

Get string from large double value(C#)

Can't find simple way to convert double to string. I need to convert large numbers without distortion. Such as:
double d = 11111111111111111111;
string s = d.ToString();
Console.WriteLine(s);
//1.11111111111111E+19
How to get string value from double value exactly the same as user enter.
11111111111111111111111 => "11111111111111111111111"
1.111111111111111111111 => "1.111111111111111111111"
Any ideas how it can be done?

double is a floating point type. So it has a limited accuracy. In your example, you could do something like this:
double d = 11111111111111111111;
string s = d.ToString("F0");
Console.WriteLine(s);
But as you'll see,this would output 11111111111111100000 instead of 11111111111111111111,so it has lost accuracy in the process. So the answer here is use the right type for the work. If you need a string, use a string variable to store the value.
Edit
This was the question i was trying to find that explains the problem with floating point math., thanks to #GSerg

First of all: 11111111111111111111111 is to large for a double value and also this value: 1.111111111111111111111 since the double max decimal length is 17.
By default, a Double value contains 15 decimal digits of precision,
although a maximum of 17 digits is maintained internally.
For this reason you should use BigInteger and then ToString for formatting the output.
There is also a library in the nuget Directory called BigRational, never used and seems in Beta stage but probably will help in solving this problem.

In general case, you can't do this: user can well input, say 123, in many a way:
123
123.00
1.23e2
12.3E1
123.0e+00
1230e-1
etc. When you convert the user input into double you loose the initial format:
string userInput = ...
// double is just 123.0 whatever input has been
double value = double.Parse(userInput);
In case you want to drop exponent if it's possible you can
double value = 11111111111111111111;
string result = value.ToString("#######################");
And, please, notice, that double has 64 bit to store the value, that's why a distortion is inevitable for large numbers:
// possible double, which will be rounded up
double big = 123456789123456789123456789.0;
// 1.2345678912345679E+26
Console.WriteLine(big.ToString("R"));
// 123456789123457000000000000
Console.WriteLine(big.ToString("###########################"));
May be you want BigInteger instead of double:
using System.Numerics;
...
BigInteger value = BigInteger.Parse("111111111111111111111111111111111");
// 111111111111111111111111111111111
Console.WriteLine(value.ToString());

C# String multiplication error

I have an assignment for TAFE in which i have to create a console program in Visual Studio that calculates the cost of a consultation based on consultation time (at $25 an hour).
string hours, rate, total;
Console.Write("Enter consultation time in hours");
hours = Console.ReadLine();
rate = ;
total = hours * rate;
Console.WriteLine("Fee is " + total);
My problem is on line 5, I get the error "operator '*' cannot be applied to operands of type 'string' and 'string;"
Can someone explain to me what is wrong, why 2 strings cant be multiplied and also supply an alternate method of getting that line to work?
EDIT: Thank you everyone. All info given was helpful. I've completed it leaving the rate as an Integer as its a set value not changed by user input, the hours and total are still strings, The hours converting to decimal via the convert.ToDecimal line GianlucaBobbio gave me. The only problem now is console doesnt stay open after calculating rate * hour, but i can fix that.
You may just have a new regular user :D! appreciate the help. you're all life savers :)

You're looking for a numeric type like int or decimal. You'll need to parse those from the input.

Console.ReadLine() returns a string so naturally, you can't multiply a string with a number. You have to parse the string as a double/int/float/decimal (whatever the case is) and then do the multiplication.
One example would be:
double hours = 0.0;
if(double.TryParse(Console.ReadLine(),out hours))
{
total = (decimal)hours * rate;
Console.WriteLine("Fee is " + total);
}
else
Console.WriteLine("You did not enter a valid number of hours.");
Since this is a calculation about money, your rate and total variables should be of type decimal.

You should convert both strings to decimal, so you can multiple them and finally convert them to string again. So you can use de Convert method.
string hours, rate, total;
Console.Write("Enter consultation time in hours");
hours = Console.ReadLine();
rate = ;
total = Convert.ToString(Convert.ToDecimal(hours) * Convert.ToDecimal(rate));
Console.WriteLine("Fee is " + total);
To handle if he puts a valid number you can use decimal.TryParse(string, decimal) which returns a bool value, and if the string is a decimal value it'll be in the out variable like decimal
string hours, rate, total;
Console.Write("Enter consultation time in hours");
hours = Console.ReadLine();
rate = ;
decimal hourInput = 0;
if(!decimal.TryParse(hours, out hourInput)
{
Console.Write("Thats not a number!");
}
else
{
total = Convert.ToString(hourInput * Convert.ToDecimal(rate));
Console.WriteLine("Fee is " + total);
}
Sorry for my bad english

C#'s type system doesn't allow for a lot of inference; unlike JavaScript or Ruby, for example, it won't implicitly convert strings to numeric types when you attempt to perform arithmetic on them. Instead, you must explicitly convert the user's input from a String to some numeric type. Here's one approach:
string hours;
decimal numericHours, rate, total;
Console.Write("Enter consultation time in hours");
hours = Console.ReadLine();
if (!Decimal.TryParse(hours, out numericHours))
{
Console.WriteLine(String.Format("{0} doesn't appear to be a valid number of hours. Please enter a numeric value.", hours));
}
else
{
rate = 35.6;
total = numericHours * rate;
Console.WriteLine("Fee is " + total);
}
That if statement deserves some further explanation: Decimal.TryParse() is one of the rare methods in the .NET framework that has two effects: it returns true or false depending on whether the first parameter can be successfully parsed as data of type decimal. The second parameter, decorated with the out keyword, will contain the resulting decimal value if the parse was successful.
A couple of bonus .NET tips: Notice the use of String.Format() to control the insertion of variables into strings - I find it nicer to use than the + string-concatenation operator. Also, as other answers have pointed out, arithmetic is performed somewhat differently on double and decimal types, due to different binary representations. When dealing with precise fractional values, especially monetary, prefer the decimal type.

C# - Separate integers/strings with division and remainder

I have a homework that I just can't figure out how to do. I'm not sure if the teacher wrote it wrong(he is a bad typer) or if there is a way to accomplish the task.
I work in Visual C# 2010 Express - Console Application
My task is to:
Read a four digit integer, such as 5893, from the keyboard and display the digits separated from one another by a tab each. Use both integer division and modulus operator % to pick off each digit. If the user enters 4567, the output looks like:
4567
4 5 6 7
Sure I know how to separate the numbers by using \t as well as reading the input and displaying it to the user. But how am I supposed to 'pick off' each digit with division and the remainder operators? Maybe he means something else, but not sure.
And another question...
How do I make sure that what the user types in is a number and not a letter?
Do I have to use Char.IsLetter, because I couldn't figure out how to use it on a parsed string.
Example:
string number1;
int x;
Console.Write("Please enter a number to calculate: ");
number1 = Console.ReadLine();
x = Int32.Parse(number1);
What method am I supposed to use and where do i put it in? Because now i only get an error and the application shuts down if I try to enter e letter.

The first question is really more about maths than programming. You know what the division and modulus operators do. Think about how you could use them to get the last (least significant) digit. Once you've done that you can apply a similar technique for the 2nd digit (tens) and then the same for hundreds and thousands and so on.
You've already found Char.IsLetter, but there is also Char.IsDigit, which does what you want more directly. You can do this check for one character and what you have is a string of characters. Have a look at a foreach loop.

System.Int32.TryParse() might be a better choice when converting the String.

Yes, your assignment makes sense. Say you have an integer x = 4567. To pick out the digit at position A you would use:
result = (int)((x / (A * 10)) % 10);
The first part of this (x / (A * 10)) "shifts" x to the right. So a value of A = 1 would divide 4567 by 10 which results in 456.7. You then use the modulo operator "%" to pick out the unit part of that number. Finally you convert to an int to remove the fractional part.

Ok, I won't give the whole solution (after all, this is homework ;)).
This code would check if there's four characters in input:
string input;
do
{
input = Console.ReadLine();
if (input.Length != 4)
Console.WriteLine("You have to enter FOUR digits");
} while (input.Length != 4);
This could be one way of checking the digits:
bool isOk = true;
foreach (char c in input.ToArray())
{
if (!Char.IsDigit(c))
{
Console.WriteLine("You have to enter four DIGITS");
isOk = false;
break;
}
}
This approach doesn't deal with math but you could do that just as well:
int num = int.Parse(input);
int tensOfThousands = num / 10000;
int thousands = (num - tensOfThousands) / 1000;
int lastDigit = num % 10;
//the rest of the digits are up to you ;)

For everybody new to C#, the solution can be simpler.
// Variables
int number = 1234;
int remainder;
string s = "";
while (number > 0) {
remainder = number % 10;
s = remainder + "\n" + s;
number /= 10;
}
Console.Write (s);