Double output problem

Okay, so here's the deal. We have a programming assignment due to calculate loan payments and then display each payment and how much they pay and how much is interest and blah,blah,blah. I'm not asking you to do the work, i've already done that. So don't treat this as the kid asking for you to do homework.

So, we come to the problem. I have two doubles of several that output with E's. I know what it's doing, it's using scientific notation. However, I don't want it to. I want it to display the number in all its glory. Here's my code, the two doubles that keep outputting with E's are amount and payment.

Code:

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#include <cmath>
#include <iostream>
#include <iomanip>

using namespace std;
     
      /*
      Name: Calc_Pmnts
      Date: 03/09/08 16:58
      Description: Calculate monthly payment
      */
      double Calc_Pmnts( double amt, double rate, int npy ){
     
        double payment,x;
     
        x = pow((1+rate),npy); //calculate (1+r)^n
     
        //calculate payment in two parts just to make sure math is carried out right
     
        payment = ((amt*x)*rate); //calculate numerator
     
        payment = payment / (x-1); //divide numerator by denominator
       
        return payment;
     
      }
     
      /*
      Name: Disp_Results
      Date: 03/09/08 16:58
      Description: Displays the final payment chart
      */
      void Disp_Results( double pmt, double rate, double amount, int npy, int totalPayments  ){
         
          cout << "\t\tAmount of Loan:\t$" << setw(11) << setprecision(3) << right << amount << endl;
          cout << "\t\tAnnual Interest Rate:\t" << setw(6) << setprecision(3) << right << rate << "%" << endl;
          cout << "\t\tPayments Per Year:\t" << setw(3) << setprecision(0) << right << npy << endl;
          cout << "\t\tTotal Number of Payments:\t" << setw(4) << setprecision(0) << right << totalPayments << endl;
          cout << "\t\tMonthly Payment:\t" << pmt << endl;
         
          system("pause");
       
      }
     
      /*
      Name: New_Loan
      Date: 03/09/08 16:58
      Description: Calculate New Loan and return number of loans processed
      */
      int New_Loan( double amt, double rate, int npy, int totalPayments, int times ){
         
          Disp_Results( Calc_Pmnts(amt,rate,npy), rate, amt, npy, totalPayments );
         
          return times+1;
         
      }

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Actual outputting is done by Disp_Results.

P.S. Yes, this is a Header file. Thus the lack of int main().

You shouldn't put using namespace std; in a header file. Also, putting your function definitions in a header isn't a good habit; it'll cause you trouble later if you try to include that header in multiple cpp files. You should only put declarations in the header, not definitions.

As to your problem, try
cout << fixed << value;

Yeah, so will that still work with this?

Code:

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cout << "text" << setw(x) << setprecision(y) << fixed << right << value << endl;

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Because our professor is adamant about our code having setw, setprecision and right in there.

Also, I added MoneyMath.cpp to my project. That contains implementations of my functions now and the .h only contains the declarations. Only thing is, I've been doing everything in .h so long i forgot. Do you include the .cpp now or the .h still?

Quote:

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Originally Posted by ccubed

Yeah, so will that still work with this?

Code:

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cout << "text" << setw(x) << setprecision(y) << fixed << right << value << endl;

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Because our professor is adamant about our code having setw, setprecision and right in there.

Also, I added MoneyMath.cpp to my project. That contains implementations of my functions now and the .h only contains the declarations. Only thing is, I've been doing everything in .h so long i forgot. Do you include the .cpp now or the .h still?

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Okay, so I put it in but now something else is happening. With fixed it makes all the doubles set to their precision. Meaning, it adds 0s. Can i stop it from adding zeros?

Quote:

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Originally Posted by Lindley

You shouldn't put using namespace std; in a header file.

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Hi Lindley,
how are ya?

The books I'm learning from do not advise against putting using namespace std in a header file. But, I saw many guys giving advice against it here on the forum many times. They just didn't explain why.

From what I can see, I frankly don't understand why I shouldn't do it. My take on why many experts advise against it is the possibility of a name collision? or re-declaration which doesn't really make sense to me either.
Even without the header guards, and we have a single header file used in multiple cpp files, I don't see why using declaration would cause problems.
So, I'm kinda lost on this one.

Can you or someone help me understand this better?
Thanks.

If you put a "using" statement in a header file, then all cpp files which include the header will inherit that statement. This completely circumvents the purpose of namespaces, which is to allow abbreviations while maintaining strict control over what they mean. If you don't have a using statement in a cpp file, you shouldn't expect that namespace to be exposed.

For my own part, I don't even put in "using namespace std;" anymore; I only put in statements for the particular parts of the namespace I'm going to use, eg "using std::vector;".

Don't know about the zeros, sorry, I use printf() much more often than cout, myself.

Quote:

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Don't know about the zeros, sorry, I use printf() much more often than cout, myself.

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Same here because TBH, the printf family of functions are infinitly easier to use for formatted output compared to streams, and make for much cleaner code.

All of your output, for example, using printf

Code:

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printf("\t\tAmount of Loan:\t$%11.3f\n", amount);
printf("\t\tAnnual Interest Rate:\t%6.3f\n", rate);
printf("\t\tPayments Per Year:\t%3i\n", npy);
printf("\t\tTotal Number of Payments:\t%4i\n", totalPayments);
printf("\t\tMonthly Payment:\t%f\n", pmt);

---

Thanks Lindley, that makes more sense.
Can I say, then, that

1. using namespace xxx technically does not causes compile or run time errors, and that it just doesn't add up with the purpose of the namespace?

2. When one of the multiple cpp files do not use the xxx, then that source file has redundancy?

and whats the zeros??

It's just bad design. It (probably) won't cause program errors unless there's actually a name collision. Say, if you had a math library and math::vector collided with std::vector because both namespaces where using'd in their respective header files.....

Quote:

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Same here because TBH, the printf family of functions are infinitly easier to use for formatted output compared to streams, and make for much cleaner code.

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The one exception I take to that is reading unknown-length string inputs. The overloads for std::string are far cleaner than trying to do everything with scanf and C-style strings. But by and large, yeah, format strings rock.

I see. Thanks

Quote:

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1. using namespace xxx technically does not causes compile or run time errors, and that it just doesn't add up with the purpose of the namespace?

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It will definetly trigger compiler errors if used improperly in a header. Consider

Code:

---

#include "HeaderWithBadUsingNamespacestdDirective.h"

#include <string>

class string
{
public:
  void Foo( ) { }
};

...

std::string text("Hello World!");
string temp;

text.clear( );
temp.Foo( ); // error here

---

If you're lucky, your compiler might give you an error about "string temp" being an ambiguous symbol. If you're not lucky, you'll just get an error that Foo() is not a member of string... and you'll soon be ready to claw your eyeballs out, since it clearly is a member of your string class.

Now, obviously a class named "string" may be an unlikely example, but there are so many names in the std namespace that you're begging for problems. Literally just yesterday on another forum I saw a topic from someone who had gotten themselves into this very problem when using a games library. The game library defined an integer type name "fixed", which was colliding with std::fixed.

Quote:

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Originally Posted by Speedo

Same here because TBH, the printf family of functions are infinitly easier to use for formatted output compared to streams, and make for much cleaner code.

All of your output, for example, using printf

Code:

---

printf("\t\tAmount of Loan:\t$%11.3f\n", amount);
printf("\t\tAnnual Interest Rate:\t%6.3f\n", rate);
printf("\t\tPayments Per Year:\t%3i\n", npy);
printf("\t\tTotal Number of Payments:\t%4i\n", totalPayments);
printf("\t\tMonthly Payment:\t%f\n", pmt);

---

---

And I wish i could use printf, though I probably could. I'm afraid he might get mad that i'm not using cout which is what he wants us to use. I'm already testing the waters with functions. I suppose I'll ask him.

Reading up on the documentation, it appears that setprecision() controls how many digits are printed after the decimal point when in fixed-point mode. If you have to call setprecision() with those values, then you're stuck with the zeros.

However, setw()'s padding can be controlled using setfill(). So if you'd like to get rid of *leading* zeroes, you should be able to use that. Since setfill()'s fill character defaults to whitespace, I'm not sure how much help that is.

So what about rounding a double to a certain number of significant figures? I know what's wrong with it. There's like 20+ decimal places in payment and i only need 2.

According to the documentation, setprecision(2) would arrange that. The rest of the padding you'd use setw() for.

Quote:

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Originally Posted by Lindley

According to the documentation, setprecision(2) would arrange that. The rest of the padding you'd use setw() for.

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I tried that, no dice. Still shows the E notation. This is really annoying. I guess i just have to go find function to round to significant figures. I could use Ceil or Floor, but I want the decimals. heh.

There's no way it should be using scientific notation if you put the fixed manipulator in there....?

of course it doesn't with Fixed. However, I want a solution that doesn't add zeros. So i'm at the point i'm hacking together a function for it. Now to figure out why converting it to a string yields xxxx.xx but converting it back to a double via istringstream yields the E notation.

Am I right in assuming that you don't want trailing zeros?

123.45
765.2
7868

instead of

123.45
765.20
7868.00

Code:

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cout << "text" << fixed << right << setw(x) << setprecision(0) << value << endl;

---

Should specify no trailing zeros. Using setprecision(2) will yield standard money notation. The rest of your formatting should be controlled via setw(); *only* the minimum number of decimal places should be controlled via setprecision().

That's what I thought. However, it doesn't work. It just gets put in scientific notation. Here's a screenshot.

http://i96.photobucket.com/albums/l190/c89c/Capture.jpg

It shows E even with 2 setprecision and setw(7).

I suppose it's possible the ordering of the manipulators matters. Try putting "fixed" both to the right and left of setprecision (alternately, not at the same time).....

Don't know what your doing but...

Code:

---

#include <iostream>
#include <iomanip>

int main()
{
        double d = 1900.0;
       
        std::cout << std::fixed << std::setw(8) << std::setprecision(2) << d << std::endl;

        return 0;
}

---

Gives me '1900.00'

Changing to std::setprecision(0) gives me '1900'

Can you show the line you are actually using rather than having us guess?

Code:

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cout << "\t\tMonthly Payment:\t" << setprecision(2) << setw(7) << pmt << endl;

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....why is std::fixed missing again? You *do* realize that all those extra zeros you were complaining about were the result of having setprecision(>2) before, don't you?

Yes, but this particular line never had setprecision greater than 2 and i've checked and it has exactly two decimal places when it's returned. For some reason, it gets retrned and then output does something weird and puts it in scientific notation.

For example:

Before Return: 1875.11
After Return: 1875.11

When I just do

Code:

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cout << pmt << endl;

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I get 1875.11. However, once it reaches the line setprecision and setw it does scientific notation for some reason.

Edit: I just tried putting fixed in and it fixes the problem. I'm still wondering why setprecision and setw would make such a difference.

http://www.cplusplus.com/reference/i...precision.html

If you don't specify fixed-point, then setprecision specifies the maximum number of meaningful digits to display. If the value is 1875.11, and you say setprecision(2), then it's only going to display 1 and 8----and the best way to do that is to write 1.8e3.

Of you do specify fixed-point, then the meaning of setprecision() changes to be the number of digits after the decimal to display.

Code:

---

double pmt = 1875.11;

cout << "\t\tMonthly Payment:\t" << setprecision(2) << setw(7) << pmt << endl;

---

Gives '1.9e+003'

Code:

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double pmt = 1875.11;

cout << "\t\tMonthly Payment:\t" << fixed << setprecision(2) << setw(7) << pmt << endl;

---

Gives '1875.11'

Quote:

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Originally Posted by Lindley

http://www.cplusplus.com/reference/i...precision.html

If you don't specify fixed-point, then setprecision specifies the maximum number of meaningful digits to display. If the value is 1875.11, and you say setprecision(2), then it's only going to display 1 and 8----and the best way to do that is to write 1.8e3.

Of you do specify fixed-point, then the meaning of setprecision() changes to be the number of digits after the decimal to display.

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Somehow, that seems like something our professor should have distinguished. He just used it like it determined decimal places and didn't affect the number at all.

When in doubt, Google. Documentation is your friend. :)