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C# Double precision subtraction should = 0 [closed]

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I've read a few posts and I understand how double arithmetic doesn't always return the results you would expect.
Why is floating point arithmetic in C# imprecise?
My problem is different though because I'm checking to see if two numbers are the same and I'm getting false when I would expect true.
I've also read this What Every Computer Scientist Should Know About Floating-Point Arithmetic, but am still having trouble understanding why two seemingly equal double variables are showing unequal.
UPDATE: They answer below helped me understand that the value displayed by the debugger wasn't the 'whole story'. That is why the two floats seemed equal. The debugger was showing equal values when hovering the variables.

Default string format is not precise for float numbers, should use "G17"
double a = 17.125 / 3.0;
double b = 17.12499999999999 / 3.0;
Console.WriteLine(a);
Console.WriteLine(b);
Console.WriteLine(a.ToString("G17"));
Console.WriteLine(b.ToString("G17"));
Console.WriteLine(a == b);
Console.WriteLine(Convert.ToString(*(long*)&a, 2));
Console.WriteLine(Convert.ToString(*(*)&b, 2));
Result:
5.70833333333333
5.70833333333333
5.708333333333333
5.7083333333333295
False
100000000010110110101010101010101010101010101010101010101010101
100000000010110110101010101010101010101010101010101010101010001
Usually to compare 2 float numbers, you can use a small error number
Console.WriteLine(Math.Abs(a - b) < 0.0000001);

Left-pad a floating point number without losing trailing zeros after decimal point [closed]

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I am attempting to write out to a fixed format text file and am having some trouble formatting the numbers properly. It needs to be padded with leading zeros and an implied decimal.
Example:
43.80
The output would need to be:
0000004380
So far, I have attempted to convert the double to a string, replace the decimal, and then pad with "0".
((amount.ToString()).Replace(".","")).PadLeft(10, '0')
The problem with this is when the number ends with zeros. The above example comes out as:
0000000438
Any suggestions?

decimal value = 34.80M;
int intVal = (int)(value * 100);
return intVal.ToString("0000000000");

You could try:
((string.Format("{0:0.00}", amount)).Replace(".","")).PadLeft(10, '0')
That way you don't lose the 2nd decimal place when the value is 0.

You can pass a .ToString() format string in as described in this article:
https://msdn.microsoft.com/en-us/library/dwhawy9k(v=vs.110).aspx
Does the incoming value always have two decimal places? If so, you could multiply by 100 to get rid of the decimal, and then to .ToString("D10")
(Int)(43.80 * 100).ToString("D10")

This should do the job : $"{(int)(amount * 100):D010}"

How to do Division in a Fractional Calculator? [closed]

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I'm completely unsure on how to do it. I've searched but can't find a simple answer.
I've done the multiplication and I know its similar to it. Need some help. I want to know how to do division for two fractions.
My Multiply module:
{
answerDenominator = num1Denominator * num2Denominator; //Multiply both denominators
answerNumerator = ((num1Whole * num1Denominator) + num1Numerator) * //multiply the whole number by the denominator and add the numerator to it
((num1Whole * num2Denominator) + num2Numerator); //multiply the whole number by the second denominator, then add the second numerator, multiply these two answers together
answerWhole = answerNumerator / answerDenominator;
answerNumerator = answerNumerator % answerDenominator;
}

Let that we have to make the following division:
(a/b):(c/d)
This is equal to
(a/b)*(d/c)
That being said the division can simply be done like below:
static double CalculateDivisionResult(double a, double b, double c, double d)
{
return (a/b)*(d/c);
}
In the above:
a is the num1Numerator.
b is the num1Denominator.
c is the num2Numerator.
d is the num2Denominator.
The most important thing that you should pay attention on the above is the fact that we use double. Why we do so?
Let that a=3, b=7, c=4 and d=5:
Then
(a/b)*(d/c) = 15/28
If you had chosen to represent your number as integers, int a=3, then the above would be obvious 0. Representing them as doubles we can overcome this.

Number to String (Always 2 decimal Place) [closed]

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I want to show a double value to label (C#) with 2 decimal places no matters that value like 13 or 13.5 or 13.505
Its always show 13.00

You can pass the format in to the to string method
eg:
ToString("0.00"); //2dp Number
ToString("n2"); // 2dp Number
ToString("c2"); // 2dp currency
http://msdn.microsoft.com/en-us/library/dwhawy9k.aspx
To change, for example, 13.505 to 13.00 you'd also want to run it through Math.Floor or use one of the other suggested methods for rounding down.
Math.Floor(value)
http://msdn.microsoft.com/en-us/library/e0b5f0xb.aspx
If, on the other hand, you want to change 13.505 to 13.50 you'd want to run it through Math.Truncate.
Math.Truncate(Value)
http://msdn.microsoft.com/en-us/library/7d101hyf(v=vs.110).aspx
So to tie that together:
Double testValue = 13.505;
Double testValueTruncated = Math.Truncate(100 * testValue) / 100;
string withDecimalPlaces = testValueTruncated.ToString("0.00");
withDecimalPlaces will now have the value "13.50"

try this method
double i=12.22222; //first variable
double j=1.2545; //second variable
double h=i*j; // multiple first and second
string s=h.ToString("0.00"); // convert to string and proper format
this methed return
s="15.33"

C# error in dividing two integers [closed]

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i have this following code to calculate the percentace in perst, but when i run this code I always get o as value in perst for all values of qxount and acount.
int perst;
int qcount;
int acount;
perst = (acount / qcount) * 100;

When dividing integers the result will be an integer. This means that you are expecting a value such as 0.75 (which you appear to be thinking you'll multiply by 100 to get a percentage) then the integer value returned will be only the 0 which is the leading integer. The remainder would be available with the % modulus operator.
However, get a percentage like you seem to want, you'll need to divide using doubles or float values.
double perst;
double qcount;
double acount;
perst = (acount / qcount) * 100;
The MSDN article on the division operator - Good idea to read.

I think you have some integer rounding issues. Try something like this.
int perst;
int qcount = 100;
int acount = 5;
perst = Convert.ToInt32(((double)acount / (double)qcount) * 100);

While rounding is almost certainly the mistake (after assigning values to the variables) the following works just fine:
int a = 62;
int b = 235;
int percentage = 100*a/b;
Console.WriteLine(percentage);
You don't need to use doubles. This rounds the percentage towards zero. If you need more precise results, go with double or single.