Ambiguous Error

[mcleano]

Doing an exercise from my C++ book and got asked to create a program that takes a double value and using a function rounds it to nearest whole value. I made my program, go the ambiguous error, so checked their code and mine happened to be more or less the same bar a few variable names, and i tried theirs and got the same problem.

Here's the code (line 16):

#include <iostream>
#include <cmath>
using namespace std;

void round(double &i);

int main()
{
    double i = 0.0;
    
    cout << "Please enter a decimal number: ";
    cin >> i;
    cin.ignore();
    
    cout << "\n\n'i' rounded to the nearest value is ";
    round(i);
    
    cout << i;
    
    cin.get();
    return 0;
}

void round(double &i)
{
     double fractpart = 0.0; intpart = 0.0;
     
     fractpart = modf(i, &intpart)
     
     if(fractpart<0.5) i = intpart;
     else intpart+=1.0;
}

I don't understand why though because there's only one function so its not like i'm overloading incorrectly. And 'i' is double like the function requires.

The error message says:
9 C:\Users\alan\Desktop\trial.cpp call of overloaded `round(double&)' is ambiguous
note C:\Dev-Cpp\include\math.h:672 candidates are: double round(double)
note C:\Dev-Cpp\include\math.h:672 void round(double&)

[Return 0]

Well, before getting to these errors, you have a few other issues to fix.

void round(double &i)
{
     double fractpart = 0.0; intpart = 0.0;
     
     fractpart = modf(i, &intpart)
     
     if(fractpart<0.5) i = intpart;
     else intpart+=1.0;
}

1. intpart has no type declared. You need to put int intpart = 0.0;
2. You're missing a semicolon at the end of this line fractpart = modf(i, &intpart)

[mcleano]

My bad, just typo's . Fixed.

[z05DSL3A]

9 C:\Users\alan\Desktop\trial.cpp call of overloaded `round(double&)' is ambiguous
note C:\Dev-Cpp\include\math.h:672 candidates are: double round(double)
note C:\Dev-Cpp\include\math.h:672 void round(double&)

Your cmath(math.h) has already got a round() function defined and can not decide on the appropriate version.

[mcleano]

Thank you Grey Wolf!

Thats quite poor tbh though with the book because thats the second time this has happened. The last time was with the variable 'count' - apparently something already in the std namespace that is called 'count. I was under the impression Herbert Schildt was one of the top programmers.

Edit: Then again maybe i'm being too harsh on possibly 'simple' mistakes. Afterall, the book is actually vary good and for such a vast amount of examples and explanations, errors are likely to occur.

[z05DSL3A]

Well, as far as I know, round() is not a standard part of cmath(math.h); so it looks like an oddity Dev C++.

[jloundy]

To round to a whole number,
simply add .5 to the number then cast it to an int.

double number = 3.6;
int round = static_cast<int>(number+.5);
cout<<"whole number = "<<round<<endl;

[Return 0]

You can always use the floor and ceil functions for rounding up and down as well.

[jloundy]

@ Return 0;

ya but note that these functions don't round the number,so ceil(.4) would return 1 and floor(.6) would return 0.
You could right a function to make these work, but i find it easier just to cast the number. Either way is fine though

[Return 0]

How does ceil and floor not round the numbers up or down?

[z05DSL3A]

Adding 0.5 and casting is not a good solution:

int round(double number)
{
    return static_cast<int>(number + 0.5);
}

int main()
{
    double a(-3.4);
    double b(-3.6);
    std::cout << a << " rounds to " << round(a) << std::endl;
    std::cout << b << " rounds to " << round(b) << std::endl;

    return 0;
}

-3.4 rounds to -2
-3.6 rounds to -3

Edit:

int round(double number)
{
    return static_cast<int>(number > 0.0 ? number + 0.5 : number - 0.5);
}

[jloundy]

I meant they dont round up if not greater then 1, so ceil(.4) = 1. But Grey wolf , some how i forgot about the existance of negitive numbers lol
here :

double num, x = .5;
int round;
cin>>num;
if(num<0)
   x = -.5;

round = static_cast<int>(num + x);
cout<<round<<endl;

seem easier then writing conditions for ceil and floor.. my opinion

[Return 0]

Yeah you're right.