C++ and sqrt() problem

ed88 · 12-04-2011, 05:45 AM

Hello to all, not much time ago i start to learnt c++ whitout teachers only whit books and tutorials ...
yestarday i had a problem whit a simple code and i don`t understand the problem, and how to fix it here my code :

Code:

#include <iostream> 
#include <math.h> 
using namespace std; 
double sq = sqrt(3); 

int main () 
{ 
double s, p, a; 
cout << "p of triangle : \n"; 
cin >> p; 
a = p / 3; 
s = (a * a * sq) / 4; 
cout << "s of triangle e : " << s << "\n"; 
return 0; 
}

Here is the error that i get if is posible to tell me how to fix it and evade it in the future :
IntelliSense: more than one instance of overloaded function "sqrt" matches the argument list: d:\visual studio 2010\projects\a\a\a.cpp 4 13 a

P.S: I use visual studio 2010

dwhitney67 · 12-04-2011, 06:02 AM

First of all, it is spelt "with", not "whit"; similarly, it is "without", not "whitout".

In your little program, and in fact in most, there is very little need to for a global variable. Thus I would recommend that you declare sq within the main() function. Also, the API for sqrt() indicates that it accepts a double-value for the parameter; you are passing an int-value. Try:

Code:

int main()
{
   const double sq = sqrt((double) 3);
   ...
}

johnsfine · 12-04-2011, 07:26 AM

Quote:

Originally Posted by ed88

more than one instance of overloaded function "sqrt"

dwhitney67 gave you most of the answer. I'll add just a little more.

You can use an integer in place of a double anywhere the compiler knows a double is required. For example, elsewhere in your program you have:

Code:

a = p / 3

That 3 needs to be a double. You provided an int. The compiler understands all that and automatically casts the int to a double.
If the only available definition of sqrt(x) required x to be a double, then sqrt(3) would work just fine. The compiler would cast the int to a double.
But there is some other definition of sqrt available, maybe sqrt(std::complex<double>). I don't recall exactly what math.h brings in and also Visual Studio header files often bring in more than they are supposed to.
Int can be cast to the input type of more than one overload of sqrt, so the compiler doesn't know which sqrt() you mean.

SigTerm · 12-04-2011, 07:52 AM

Quote:

Originally Posted by ed88

Code:

using namespace std;

Remove "using namespace std" - it is a very bad habit.
Put "using std::cout;" into main() instead of that:

Code:

int main(int argc, char** argv){ 
    using std::cout; 
    //...
}

Quote:

Originally Posted by dwhitney67

[code]
int main()
{
const double sq = sqrt((double) 3);
...
}

I'd recommend

Code:

int main(){
   const double sq = sqrt(3.0);
   ...
}

"3" is an int.
"3.0" - double.
"3.0f" - float.

Quote:

Originally Posted by johnsfine

I don't recall exactly what math.h brings in

In such situation cl.exe (visual studio compiler, obviously) normally lists possible candidates within compiler output right under error message:

Code:

error C2668: 'sqrt' : ambiguous call to overloaded function
	math.h(581): could be 'long double sqrt(long double)'
	math.h(533): or       'float sqrt(float)'
	math.h(128): or       'double sqrt(double)'
        while trying to match the argument list '(int)'

ed88 · 12-07-2011, 08:24 AM

Thanks of all
if (some one have someting to add)
will be nice

else
Thanks again