My mind is baffled by this simple equation in C#

Question

I've got a problem. I'm attempting to make a Farenheit to Celcius calculator, and when I do the fraction part of math, it kinda doesn't work. It's either 0 or 1.

private void toCelcius_Click(object sender, EventArgs e)
{
    double F = double.Parse(temperatureBox.Text);
    double fm32 = F - 32;
    double fraction = (9 / 5);
    double newTemp = fraction*fm32;

    temperatureLabel.Text = newTemp.ToString();
}

I've been using 100 as my test number, and everytime I send 100 to the textbox, it returns 68. It should be somewhere around 30ish.

Currently the program only senses the fraction as a 1. I tried using decimal instead of using double, but that breaks the newTemp problem. I tried using float, but got same results as a double. I have no freaking idea whats going on but it's very frustrating.

If anyone knows how to fix this, I'd be very thankful.

EDIT: Facepalm it's been such a long time since I've used doubles, forgot I needed to have the .0 after each number.

yea.. I noticed that after I submitted it, but either way, it didn't give the right answer — John Olivas, Jan 28 '16 at 02:53

Ian · Answer 1 · 2016-01-28T03:06:17.573

5

You should put double for your number:

private void toCelcius_Click(object sender, EventArgs e)
{
    double F = double.Parse(temperatureBox.Text);
    double fm32 = F - 32;
    double fraction = ((double)9 / 5);
    double newTemp = fraction*fm32;

    temperatureLabel.Text = newTemp.ToString();
}

Otherwise, 9 will be read as int since this is the base C# literal for number (without comma or any other suffix like D). That is why you always get fraction as 1 because: 9/5 = 1.8 will be read as 1 in int

Alternatively, you could do this:

double fraction = (9D / 5); //the shortest (credit for Coxy)

Or, for more readability:

double fraction = (9.0 / 5); //like what we have in math (as pointed out by Michael Burr)

edited Jan 28 '16 at 03:06

answered Jan 28 '16 at 02:50

Ian

30,182
19
69
107

Oh.. I'll try that. Thanks – John Olivas Jan 28 '16 at 02:51
yea I feel dumb, that worked haha thank you :) – John Olivas Jan 28 '16 at 02:52
`9D` may be more readable than `(double)9`. – Coxy Jan 28 '16 at 02:54
@Coxy yes, that would have been the shortest answer. :) I merely show the necessity of casting without considering the shortest way (edited) – Ian Jan 28 '16 at 02:56
Wouldn't `9.0` be even more readable? – Michael Burr Jan 28 '16 at 02:56

score 2 · Answer 2 · answered Jan 28 '16 at 02:53

2

Alternatively use;

Double fraction = 9.0 / 5.0;

answered Jan 28 '16 at 02:53

John Hascall

9,176
6
48
72

yea, I forgot I had to use the .0's after each number for a double.. lol - thanks – John Olivas Jan 28 '16 at 02:57
@JohnOlivas actually for you case, you only need to put `.0` for any **one** of the numbers, the other will be automatically promoted for operation. But writing in both for readability is fine too. ;) – Ian Jan 28 '16 at 03:08

My mind is baffled by this simple equation in C#

2 Answers2