How to round off the numbers to 2 decimal places?

Question

I end up getting -0.944444444444444 when I want it to be -0.94 Assuming the entered temperature is 30.3 and clicking Fahrenheit to Celsius.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace TemperatureConverter
{
    public partial class FrmTemperature : Form
    {
        public FrmTemperature()
        {
            InitializeComponent();
        }

        private void btnCalcFahrenheit_Click(object sender, EventArgs e)
        {
            lblFahrenheit.Text = Convert.ToString(9.0/5.0 * Convert.ToDouble(txtTemperature.Text) + 32.0);
        }

        private void btnCalcCelsius_Click(object sender, EventArgs e)
        {
            lblCelsius.Text = Convert.ToString(5.0/9.0*(Convert.ToDouble(txtTemperature.Text) - 32.0));
        }
    }
}

@ChristianGollhardt I've read up on it and tried a couple of different ways but can't seem to get the answer. That's why I posted my own. — Chibbie, Jan 17 '17 at 00:36
What does not work, e.g. what mean does not work? Please edit your question and explain with a [MCVE](http://stackoverflow.com/help/mcve) exactly what does not work. What compiler/runtime error do you get? — Christian Gollhardt, Jan 17 '17 at 00:46
@ChristianGollhardt I get what I stated in my post. -0.944444444444 — Chibbie, Jan 17 '17 at 00:47
So you get with `(-0.944444444444).ToString("#.##")` the value `"-0.944444444444"` instead of `"-0.94"`? This seems like a bug then. — Christian Gollhardt, Jan 17 '17 at 00:49
Also see [this fiddle](https://dotnetfiddle.net/B7vZke), which seems to perfectly work. — Christian Gollhardt, Jan 17 '17 at 00:52
@ChristianGollhardt I figured out the issue I tried the .ToString at the end but didn't remove the Convert.ToString infront of the calculation. — Chibbie, Jan 17 '17 at 00:52

score 2 · Accepted Answer · answered Jan 17 '17 at 00:38

2

Use ToString method like following:

(5.0/9.0*(Convert.ToDouble(txtTemperature.Text) - 32.0)).ToString("0.00");

I also suggest you parse the temperature text as a separate step to show user errors.

e.g.

double temp;
if (double.TryParse(txtTemperature.Text, out temp))
    lblCelsius.Text = (5.0/9.0*(temp - 32.0)).ToString("0.00");
else
    // Show error to user

answered Jan 17 '17 at 00:38

Bishoy

705
9
24

2

Please refer, [how to handle duplicates](http://meta.stackexchange.com/questions/10841/how-should-duplicate-questions-be-handled). – Christian Gollhardt Jan 17 '17 at 00:41

score 1 · Answer 2 · answered Jan 17 '17 at 00:41

Perhaps use string.Format() or string interpolation (new feature in C# 6.0).

Using string.Format()

private void btnCalcFahrenheit_Click(object sender, EventArgs e)
{
    var fahrenheit = 9.0/5.0 * Convert.ToDouble(txtTemperature.Text) + 32.0;
    lblFahrenheit.Text = string.Format("{0:N0}", fahrenheit);
}
private void btnCalcCelsius_Click(object sender, EventArgs e)
{
    var celsius = 5.0/9.0*(Convert.ToDouble(txtTemperature.Text) - 32.0);
    lblCelsius.Text = string.Format("{0:N0}", celsius);
}

Using string interpolation:

private void btnCalcFahrenheit_Click(object sender, EventArgs e)
{
    var fahrenheit = 9.0/5.0 * Convert.ToDouble(txtTemperature.Text) + 32.0;
    lblFahrenheit.Text = $"{fahrenheit:N2}";
}
private void btnCalcCelsius_Click(object sender, EventArgs e)
{
    var celsius = 5.0/9.0*(Convert.ToDouble(txtTemperature.Text) - 32.0);
    lblCelsius.Text = $"{celsius:N2}";
}

Note that the formatter "N2" will format the number using your selected locale's radix and separator character. For US-EN, that will be "." for radix and "," for separator. For instance, 1295.422 degrees would be formatted as 1,295.42.

How to round off the numbers to 2 decimal places?

2 Answers2