Using Math::Round

Question

I have the following visual c++ code

#include <iostream>
#include <string>
#include <sstream>
#include <math.h>

using namespace std;

int Main()
{
    double investment = 0.0;
    double newAmount = 0.0;
    double interest = 0.0;
    double totalSavings = 0.0;
    int month = 1;
    double interestRate = 0.065;

    cout << "Month\tInvestment\tNew Amount\tInterest\tTotal Savings";
    while (month < 10)
    {
            investment = investment + 50.0;
        if ((month % 3 == 0))
        {
          interest = Math::Round((investment * Math::Round(interestRate/4, 2)), 2);
        }
        else
        {
          interest = 0;
        }
        newAmount = investment + interest;
        totalSavings = newAmount;
        cout << month << "\t" << investment << "\t\t" << newAmount << "\t\t" << interest << "\t\t" << totalSavings;
        month++;
    }
  string mystr = 0;
  getline (cin,mystr);
  return 0;
}

But its giving me problems using Math::Round, truly I don't know how to use this function using visual c++

score 7 · Answer 1 · answered Nov 16 '09 at 20:24

7

Math::Round() is .NET, not C++.

I don't believe there is a direct equal in C++.

You can write your own like this (untested):

double round(double value, int digits)
{
  return floor(value * pow(10, digits) + 0.5) / pow(10, digits);
}

answered Nov 16 '09 at 20:24

Aaron

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As far as I can tell this does not work and in general rolling your own version of [round is hard to do correctly](http://stackoverflow.com/a/24348037/1708801). – Shafik Yaghmour Jul 03 '14 at 02:48

Swiss · Answer 2 · 2014-07-03T19:13:34.173

6

Unfortunately Math::Round is part of the .NET framework and is not part of the normal C++ spec. There are two possible solutions to this.

The first is to implement the round function yourself, using either ceil or floor from <cmath> and creating a function similar to the following.

#include <cmath>
inline double round(double x) { return (floor(x + 0.5)); }

The second is to enable Common Language Runtime (CLR) support for your C++ program, which will allow access to the .NET framework, but at the cost of having it no longer be a true C++ program. If this is just a small program for your own use, this probably isn't a big deal.

To enable CLR support, do the following:

Right click your solution and click properties. Then click Configuration Properties -> General -> Project Defaults. Under Common Language Runtime support, choose the option Common Language Runtime Support (/clr). Then click Apply and OK.

Next, add the following to the top of your code:

using namespace System;

Now you should be able to use Math::Round as with any other .NET language.

edited Jul 03 '14 at 19:13

answered Nov 16 '09 at 20:24

Swiss

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Your version of round has two issues, there are values for while adding `.5` won't work and truncating to `int` has overflow issues. I explain both in my [answer here](http://stackoverflow.com/a/24348037/1708801). Boost is a viable alternative for older systems. – Shafik Yaghmour Jul 03 '14 at 02:29
1

@ShafikYaghmour Nice catch with the type problems. As for the algorithm itself, that's a huge discussion way outside the scope of this question. I will say the algorithm is very common and should be sufficient for the needs expressed here. – Swiss Jul 03 '14 at 19:20
It fails for certain values including `0.49999999999999994`, [see it live](http://coliru.stacked-crooked.com/a/e8c613b87fc742ca) – Shafik Yaghmour Jul 04 '14 at 01:29

Scott · Answer 3 · 2014-04-02T19:59:01.967

4

Just ran into this, and it is now 2013.

This is supported in C11, not older versions. So yes, the approved answer was appropriate in '09.

If you are using C11 and you do

    include <math.h>

you should be able to call "round",

Such that:

    double a = 1.5;
    round(a);

Resulting in:

    a == 1.0

edited Apr 02 '14 at 19:59

answered Apr 02 '14 at 19:01

Scott

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2

just commenting that the edits were purely for clarity and to correct some formatting. – Scott Apr 02 '14 at 20:02
1

Still this just work if you're using VC12 or higher compiler. (Visual Studio 2013 or newer) – Gustavo Maciel Jun 12 '14 at 00:35

score 0 · Answer 4 · answered Nov 16 '09 at 20:22

0

AFAICT cmath (math.h) doesn't define a Round function, nor a Math namespace. see http://msdn.microsoft.com/en-us/library/7wsh95e5%28VS.80,loband%29.aspx

answered Nov 16 '09 at 20:22

just somebody

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I think he's trying to use this: http://msdn.microsoft.com/en-us/library/75ks3aby.aspx – John D. Nov 16 '09 at 20:24

score 0 · Answer 5 · answered Nov 16 '09 at 20:25

0

You might be better off adding 0.5 and using floor() as mentioned in another post here to get basic rounding.

answered Nov 16 '09 at 20:25

DanDan

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Using Math::Round

5 Answers5