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Replacing float with int - how do I do localized input/output?

This is one of those cases where I assume the solution is on google, but I have no idea what the search term even is. Or even which Tags to use on Stack Overflow.
Situation:
Floats are not precise. A common trick around it, is to use Integers for the math, then shift the decimal point during output:
If you need 4 decimal places of precision for € (not uncommon in finances), you effectively measure and calculate in milli-Euro. Then during output you shift the decimal left, and cut off the last 2 digits:
So a int 1234567 that is stored, retrieved and processes as a int, would print as/stand for "123.45 €" to the normal end user.
Problem:
But how would this interact with localisation? .NET has this awesome part where Parse() and ToString() look at the current Windows Users Culture setting, to figure out what the decimal separator, group separator and group size is today.
There seems to be no fixed point type in .NET, to do the work for me.
Is there some format string combination I could use to say "shift decimal point 4 left into the number, omit last 2 digits)"? F2 would only add two empty 0 past the decimal point for any int. and "1234567.00 €" is a few orders of magnitude off from "123.45 €"
My best idea thus far:
Building my own format string out of the NumberDecimalSeparator, NumberGroupSeparator and NumberGroupSizes from the users culture - but that is just ugly and seems like something I should not be doing. Is there a better day to do it, or is it one of those cases where I have to go for the ugly thing that works?

Maybe something like this
using System.Globalization;
int n = 123456;
string price = "";
string priceW = "";
int i = 0;
foreach(char c in n.ToString())
{
i++;
if(i == n.ToString().Length - 1)
price += ".";
price += c;
}
float rPrice = float.Parse(price, CultureInfo.InvariantCulture.NumberFormat);
priceW = price + "€";

c# large fractional decimal split

My Requirement is Fractional Amount FIrst 2 decimal part add customer bank account and others fractional part add in dispute wallet account .
var amount = 40.235667745465465
I want to convert it 2 different variable
var customerBalance = // ??? - should be 40.23
var disputeBalance = amount - customerBalance
How can I do calculate the step marked ??? ?

This will work fine.
var firstAmount = Math.Floor(amount / 0.01) / 100 ;
var secondVariable = amount - firstAmount;

You probably want:
var firstAmount = Math.Round(amount, 2);
but note that this can round up as well as down; you may want to check whether secondVariable comes out negative, and if so: compensate.
Another way to look at it is to multiply by 100 and take the integer/decimal parts (hint: Math.Floor), then divide by 100 again.

If you are looking for a string, then it can be:
string secondVariableAsString = string.Format("{0:0.00}", secondVariable);
Another is:
Math.Truncate(100 * secondVariable) / 100;
However, this will cause overflow for large numbers.

What is the sum of the digits of the number 2^1000?

This is a problem from Project Euler, and this question includes some source code, so consider this your spoiler alert, in case you are interested in solving it yourself. It is discouraged to distribute solutions to the problems, and that isn't what I want. I just need a little nudge and guidance in the right direction, in good faith.
The problem reads as follows:
2^15 = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.
What is the sum of the digits of the number 2^1000?
I understand the premise and math of the problem, but I've only started practicing C# a week ago, so my programming is shaky at best.
I know that int, long and double are hopelessly inadequate for holding the 300+ (base 10) digits of 2^1000 precisely, so some strategy is needed. My strategy was to set a calculation which gets the digits one by one, and hope that the compiler could figure out how to calculate each digit without some error like overflow:
using System;
using System.IO;
using System.Windows.Forms;
namespace euler016
{
class DigitSum
{
// sum all the (base 10) digits of 2^powerOfTwo
[STAThread]
static void Main(string[] args)
{
int powerOfTwo = 1000;
int sum = 0;
// iterate through each (base 10) digit of 2^powerOfTwo, from right to left
for (int digit = 0; Math.Pow(10, digit) < Math.Pow(2, powerOfTwo); digit++)
{
// add next rightmost digit to sum
sum += (int)((Math.Pow(2, powerOfTwo) / Math.Pow(10, digit) % 10));
}
// write output to console, and save solution to clipboard
Console.Write("Power of two: {0} Sum of digits: {1}\n", powerOfTwo, sum);
Clipboard.SetText(sum.ToString());
Console.WriteLine("Answer copied to clipboard. Press any key to exit.");
Console.ReadKey();
}
}
}
It seems to work perfectly for powerOfTwo < 34. My calculator ran out of significant digits above that, so I couldn't test higher powers. But tracing the program, it looks like no overflow is occurring: the number of digits calculated gradually increases as powerOfTwo = 1000 increases, and the sum of digits also (on average) increases with increasing powerOfTwo.
For the actual calculation I am supposed to perform, I get the output:
Power of two: 1000 Sum of digits: 1189
But 1189 isn't the right answer. What is wrong with my program? I am open to any and all constructive criticisms.

For calculating the values of such big numbers you not only need to be a good programmer but also a good mathematician. Here is a hint for you,
there's familiar formula ax = ex ln a , or if you prefer, ax = 10x log a.
More specific to your problem
21000 Find the common (base 10) log of 2, and multiply it by 1000; this is the power of 10. If you get something like 1053.142 (53.142 = log 2 value * 1000) - which you most likely will - then that is 1053 x 100.142; just evaluate 100.142 and you will get a number between 1 and 10; and multiply that by 1053, But this 1053 will not be useful as 53 zero sum will be zero only.
For log calculation in C#
Math.Log(num, base);
For more accuracy you can use, Log and Pow function of Big Integer.
Now rest programming help I believe you can have from your side.

Normal int can't help you with such a large number. Not even long. They are never designed to handle numbers such huge. int can store around 10 digits (exact max: 2,147,483,647) and long for around 19 digits (exact max: 9,223,372,036,854,775,807). However, A quick calculation from built-in Windows calculator tells me 2^1000 is a number of more than 300 digits.
(side note: the exact value can be obtained from int.MAX_VALUE and long.MAX_VALUE respectively)
As you want precise sum of digits, even float or double types won't work because they only store significant digits for few to some tens of digits. (7 digit for float, 15-16 digits for double). Read here for more information about floating point representation, double precision
However, C# provides a built-in arithmetic
BigInteger for arbitrary precision, which should suit your (testing) needs. i.e. can do arithmetic in any number of digits (Theoretically of course. In practice it is limited by memory of your physical machine really, and takes time too depending on your CPU power)
Back to your code, I think the problem is here
Math.Pow(2, powerOfTwo)
This overflows the calculation. Well, not really, but it is the double precision is not precisely representing the actual value of the result, as I said.

A solution without using the BigInteger class is to store each digit in it's own int and then do the multiplication manually.
static void Problem16()
{
int[] digits = new int[350];
//we're doing multiplication so start with a value of 1
digits[0] = 1;
//2^1000 so we'll be multiplying 1000 times
for (int i = 0; i < 1000; i++)
{
//run down the entire array multiplying each digit by 2
for (int j = digits.Length - 2; j >= 0; j--)
{
//multiply
digits[j] *= 2;
//carry
digits[j + 1] += digits[j] / 10;
//reduce
digits[j] %= 10;
}
}
//now just collect the result
long result = 0;
for (int i = 0; i < digits.Length; i++)
{
result += digits[i];
}
Console.WriteLine(result);
Console.ReadKey();
}

I used bitwise shifting to left. Then converting to array and summing its elements. My end result is 1366, Do not forget to add reference to System.Numerics;
BigInteger i = 1;
i = i << 1000;
char[] myBigInt = i.ToString().ToCharArray();
long sum = long.Parse(myBigInt[0].ToString());
for (int a = 0; a < myBigInt.Length - 1; a++)
{
sum += long.Parse(myBigInt[a + 1].ToString());
}
Console.WriteLine(sum);

since the question is c# specific using a bigInt might do the job. in java and python too it works but in languages like c and c++ where the facility is not available you have to take a array and do multiplication. take a big digit in array and multiply it with 2. that would be simple and will help in improving your logical skill. and coming to project Euler. there is a problem in which you have to find 100! you might want to apply the same logic for that too.

Try using BigInteger type , 2^100 will end up to a a very large number for even double to handle.

BigInteger bi= new BigInteger("2");
bi=bi.pow(1000);
// System.out.println("Val:"+bi.toString());
String stringArr[]=bi.toString().split("");
int sum=0;
for (String string : stringArr)
{ if(!string.isEmpty()) sum+=Integer.parseInt(string); }
System.out.println("Sum:"+sum);
------------------------------------------------------------------------
output :=> Sum:1366

Here's my solution in JavaScript
(function (exponent) {
const num = BigInt(Math.pow(2, exponent))
let arr = num.toString().split('')
arr.slice(arr.length - 1)
const result = arr.reduce((r,c)=> parseInt(r)+parseInt(c))
console.log(result)
})(1000)

This is not a serious answer—just an observation.
Although it is a good challenge to try to beat Project Euler using only one programming language, I believe the site aims to further the horizons of all programmers who attempt it. In other words, consider using a different programming language.
A Common Lisp solution to the problem could be as simple as
(defun sum_digits (x)
(if (= x 0)
0
(+ (mod x 10) (sum_digits (truncate (/ x 10))))))
(print (sum_digits (expt 2 1000)))

main()
{
char c[60];
int k=0;
while(k<=59)
{
c[k]='0';
k++;
}
c[59]='2';
int n=1;
while(n<=999)
{
k=0;
while(k<=59)
{
c[k]=(c[k]*2)-48;
k++;
}
k=0;
while(k<=59)
{
if(c[k]>57){ c[k-1]+=1;c[k]-=10; }
k++;
}
if(c[0]>57)
{
k=0;
while(k<=59)
{
c[k]=c[k]/2;
k++;
}
printf("%s",c);
exit(0);
}
n++;
}
printf("%s",c);
}

Python makes it very simple to compute this with an oneliner:
print sum(int(digit) for digit in str(2**1000))
or alternatively with map:
print sum(map(int,str(2**1000)))

Longest recurring cycle in its decimal fraction - a bug or a misunderstanding?

This is fairly 'math-y' but I'm posting here because it's a Project Euler problem, & I have working code that presumably has bugs in it.
The question Determing longest repeating cycle in a decimal expansion solves the problem using logarithms, but I'm interested in solving with simple brute force. More accurately, I'm interested in understanding why my algorithm and code is not returning the correct solution.
The algorithm is simple:
replicate a 'long division',
at each step record the divisor and the remainder
when a divisor / remainder tuple is repeated, infer that the decimal representation will repeat.
Here are private fields, as requested
private int numerator;
private int recurrence;
private int result;
private int resultRecurrence;
private List<dynamic> digits;
and here is the code:
private void Go()
{
foreach (var i in primes)
{
digits = new List<dynamic>();
numerator = 1;
recurrence = 0;
while (numerator != 0)
{
numerator *= 10;
// quotient
var q = numerator / i;
// remainder
var r = numerator % i;
digits.Add(new { Divisor = q, Remainder = r });
// if we've found a repetition then break out
var m = digits.Where(p => p.Divisor == q && p.Remainder == r).ToList();
if (m.Count > 1)
{
recurrence = digits.LastIndexOf(m[0]) - digits.IndexOf(m[0]);
break;
}
numerator = r;
}
if (recurrence > resultRecurrence)
{
resultRecurrence = recurrence;
result = i;
}
}}
When testing integers < 10 and < 20 I get the correct result; and I correctly identify the value of i as well. However the decimal represetation that I get is incorrect - I calculate i-1 whereas the correct result is far less (something like i-250).
So presumably I either have a programming bug - which I can't find - or a logic bug.
I'm confused because it feels like a multiplicative group over p to me, in which there would be p-1 elements. I'm sure I'm missing something, can anyone provide suggestions?
edit
I'm not going to include my prime number code - it's not relevant, as I explain above I correctly identify the value of i (from memory it is 983) but I'm having problems getting the correct value for resultRecurrence.

I'm confused because it feels like a multiplicative group over p to me, in which there would be p-1 elements. I'm sure I'm missing something, can anyone provide suggestions?
Close.
For all primes except 2 and 5 (which divide 10), the sequence of remainders is formed by starting with 1 and transforming by
remainder = (10 * remainder) % prime
thus the k-th remainder is 10k (mod prime) and the set of remainders forms a subgroup of the group of nonzero remainders modulo prime[1]. The length of the recurring cycle is the order of that subgroup, which is also known as the order of 10 modulo prime.
The order of the group of nonzero remainders modulo prime is prime-1, and there's a theorem by Fermat:
Let G be a finite group of order g and H be a subgroup of G. Then the order h of H divides g.
So the length of the cycle is always a divisor of prime-1, and sometimes it's prime-1, e.g. for 7 or 19.
[1] For composite numbers n coprime to 10, that would be the group of remainders modulo n that are coprime to n.

First off, you don’t need the divisors, you only need the remainders.
Secondly, I would split the function into multiple independent parts instead of having everything in one big method: The long division / finding of the cycle length is independent of the rest (= finding the longest cycle).
Your break on Where coupled with Count is unintuitive. Why not just use a while loop with the condition (! digits.Contains(r))? (This would require putting 0 as a remainder into the digits list before the loop start.)
This leaves us with a much cleaner code that should be straightforward to debug.

recurrence = digits.LastIndexOf(m[0]) - digits.IndexOf(m[0]);
Surely the value of resultRecurrence is always going to be i-1 ? Since for a fraction of the form 1/n, the decimal starts repeating exactly when the division-in-progress (the ith digit) gives the same quotient-remainder as the very first trial division (1, hence i-1).
(as a side note, may I introduce you to Math.DivRem).

Series calculation

I have some random integers like
99 20 30 1 100 400 5 10
I have to find a sum from any combination of these integers that is closest(equal or more but not less) to a given number like
183
what is the fastest and accurate way of doing this?

If your numbers are small, you can use a simple Dynamic Programming(DP) technique. Don't let this name scare you. The technique is fairly understandable. Basically you break the larger problem into subproblems.
Here we define the problem to be can[number]. If the number can be constructed from the integers in your file, then can[number] is true, otherwise it is false. It is obvious that 0 is constructable by not using any numbers at all, so can[0] is true. Now you try to use every number from the input file. We try to see if the sum j is achievable. If an already achieved sum + current number we try == j, then j is clearly achievable. If you want to keep track of what numbers made a particular sum, use an additional prev array, which stores the last used number to make the sum. See the code below for an implementation of this idea:
int UPPER_BOUND = number1 + number2 + ... + numbern //The largest number you can construct
bool can[UPPER_BOUND + 1]; //can[number] is true if number can be constructed
can[0] = true; //0 is achievable always by not using any number
int prev[UPPER_BOUND + 1]; //prev[number] is the last number used to achieve sum "number"
for (int i = 0; i < N; i++) //Try to use every number(numbers[i]) from the input file
{
for (int j = UPPER_BOUND; j >= 1; j--) //Try to see if j is an achievable sum
{
if (can[j]) continue; //It is already an achieved sum, so go to the next j
if (j - numbers[i] >= 0 && can[j - numbers[i]]) //If an (already achievable sum) + (numbers[i]) == j, then j is obviously achievable
{
can[j] = true;
prev[j] = numbers[i]; //To achieve j we used numbers[i]
}
}
}
int CLOSEST_SUM = -1;
for (int i = SUM; i <= UPPER_BOUND; i++)
if (can[i])
{
//the closest number to SUM(larger than SUM) is i
CLOSEST_SUM = i;
break;
}
int currentSum = CLOSEST_SUM;
do
{
int usedNumber = prev[currentSum];
Console.WriteLine(usedNumber);
currentSum -= usedNumber;
} while (currentSum > 0);

This seems to be a Knapsack-like problem, where the value of your integers would be the "weight" of each item, the "profit" of each item is 1, and you are looking for the least number of items to exactly sum to the maximum allowable weight of the knapsack.

This is a variant of the SUBSET-SUM problem, and is also NP-Hard like SUBSET-SUM.
But if the numbers involved are small, pseudo-polynomial time algorithms exist. Check out:
http://en.wikipedia.org/wiki/Subset_sum_problem
Ok More details.
The following problem:
Given an array of integers, and integers a,b, is there
some subset whose sum lies in the
interval [a,b] is NP-Hard.
This is so because we can solve subset-sum by choosing a=b=0.
Now this problem easily reduces to your problem and so your problem is NP-Hard too.
Now you can use the polynomial time approximation algorithm mentioned in the wiki link above.
Given an array of N integers, a target S and an approximation threshold c,
there is a polynomial time approximation algorithm (involving 1/c) which tells if there is a subset sum in the interval [(1-c)S, S].
You can use this repeatedly (by some form of binary search) to find the best approximation to S you need. Note you can also use this on intervals of the from [S, (1+c)S], while the knapsack will only give you a solution <= S.
Of course there might be better algorithms, in fact I can bet on it. There should be plenty of literature on the web. Some search terms you can use: approximation algorithms for subset-sum, pseudo-polynomial time algorithms, dynamic programming algorithm etc.

A simple-brute-force-method would be to read the text in, parse it into numbers, and then go through all combinations until you find the required sum.
A quicker solution would be to sort the numbers, then...
Add the largest number to your sum, Is it too big? if so, take it off and try the next smallest.
if the sum is too small, add the next largest number and repeat.
Continue adding numbers not letting the sum exceed the target. Finish when you hit the target.
Note that when you backtrack, you may need to back track more than one level. Sounds like a good case for recursion...

If the numbers are large you can turn this into an Integer Programme. Using Mathematicas solver, it might look something like this
nums = {99, 20, 30 , 1, 100, 400, 5, 10};
vars = a /# Range#Length#nums;
Minimize[(vars.nums - 183)^2, vars, Integers]

You can sort the list of values, find the first value that's greater than the target, and start concentrating on the values that are less than the target. Find the sum that's closest to the target without going over, then compare that to the first value greater than the target. If the difference between the closest sum and the target is less than the difference between the first value greater than the target and the target, then you have the sum that's closest.
Kinda hokey, but I think the logic hangs together.