Author 
Message 
jhooper3581

Posted: Mon Aug 31, 2009 2:17 am Post subject: Write the source code 


Write a C++ source code that will read an input of radius of a circle and outputs the area of the circle. 





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jhooper3581

Posted: Mon Aug 31, 2009 2:28 am Post subject: (No subject) 


My solution.
code:  #include <iostream>
#include <cmath>
using namespace std;
int main()
{
// Mathematically it's obvious that r >= 0, where r is the radius.
double r;
cout << "Enter a radius where it is greater than or equal to 0: ";
cin >> r;
const double PI(3.1416);
double area(PI * pow(r, 2));
cout << "The area of the circle with radius " << r << " is " << area << "." << endl;
system("PAUSE");
return 0;
}

If any other interesting solutions are available, please post them. 





saltpro15

Posted: Mon Aug 31, 2009 8:03 am Post subject: RE:Write the source code 


Nice. My only recommendation is to use a longer value of Pi, as really, really big numbers could give you precision errors. I like to use the first 9 digits. 





Insectoid

Posted: Mon Aug 31, 2009 8:20 am Post subject: RE:Write the source code 


Is ^ not a function in C++? I notice you use pow(x, 2) which I assume means x^2. How hard IS it to put that into a language? (Or is it already reserved for a different command?) 





saltpro15

Posted: Mon Aug 31, 2009 8:38 am Post subject: RE:Write the source code 


in C++ "^" is used as XOR.
and why the heck would you not just use x * x ? 





A.J

Posted: Mon Aug 31, 2009 8:48 am Post subject: RE:Write the source code 


You could also output the area to a given number of decimal places like so:
c++: 
#include <iostream>
#include <cmath>
using namespace std;
double r, area;
int DecimalPlaces;
int main()
{
cout << "Enter a radius where it is greater than or equal to 0: " << endl;
cin >> r;
cout << "To how many decimal places do you want the area to be given to you?" << endl;
cin >> DecimalPlaces;
area = M_PI * (r*r);
cout << "The area of the circle with radius " << r << " is ";
cout.setf (ios_base::fixed, ios_base::floatfield);
cout.precision (DecimalPlaces);
cout << area << "." << endl;
system ("PAUSE");
return 0;
}

(Note: M_PI is a builtin constant that can be accessed by importing cmath/math.h) 





saltpro15

Posted: Mon Aug 31, 2009 8:57 am Post subject: Re: Write the source code 


Just because I'm waiting for my pancakes to finish cooking, here's another version
c++: 
#include<cstdio>
#include<cmath>
double r, area;
main()
{
printf("Enter a radius greater than or equal to 0\n");
scanf("%f", &r); // scanf needs a pointer when inputting variables, hence &r instead of r
area= M_PI * (r*r);
printf("%.5f\n", area); // the .5 will print to 5 decimal places
}







DtY

Posted: Mon Aug 31, 2009 10:47 am Post subject: Re: RE:Write the source code 


insectoid @ Mon Aug 31, 2009 8:20 am wrote: Is ^ not a function in C++? I notice you use pow(x, 2) which I assume means x^2. How hard IS it to put that into a language? (Or is it already reserved for a different command?)
I believe the reason that there is no power operator in C/++ is because there's no good way to implement it (that works with decimals and all that), and giving an operator will make people dependant on it (like using x**2 instead of x*x), instead it's a lot more work to #include <math.h> and then link it with the math library (if you want to do decimal powers) 





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CodeMonkey2000

Posted: Mon Aug 31, 2009 2:21 pm Post subject: Re: RE:Write the source code 


insectoid @ Mon Aug 31, 2009 8:20 am wrote: Is ^ not a function in C++? I notice you use pow(x, 2) which I assume means x^2. How hard IS it to put that into a language? (Or is it already reserved for a different command?)
As saltpro15 already said, ^ is the XOR operation. The function pow is part of the cmath library, which is a C library. You could theoretically create your own number class, and overload the ^ operator for powers. Like so:
c++: 
#include <iostream>
#include <cmath>
class INT
{
public:
//does all standard operations like a good integer should
INT();
INT(int value) {val=value;}
INT operator*(INT other) const {return INT(val*other.val);}
INT operator/(INT other) const {return INT(val/other.val);}
INT operator+(const INT &other) const {return INT(val+other.val);}
INT operator(const INT &other) const {return INT(valother.val);}
INT operator^(const INT &other) const {return INT((int)pow((double)val,(double)other.val));}
INT operator() const {return INT(val*1);}
const INT &operator*=(const INT &other){val*=other.val; return *this;}
const INT &operator/=(const INT &other){val/=other.val; return *this;}
const INT &operator+=(const INT &other){val+=other.val; return *this;}
const INT &operator=(const INT &other){val=other.val; return *this;}
const INT &operator=(const INT &other){val=other.val; return *this;}
//some code shamelessly stolen from wtd
friend std::ostream& operator<<(std::ostream& out, const INT& other);
private:
int val;
};
std::ostream& operator<<(std::ostream& out, const INT& other)
{
return out <<other.val;
}
int main()
{
INT a=2;
INT b=3;
std::cout<<"a="<<a<<std::endl
<<"b="<<b<<std::endl
<<"a+b="<<(a+b)<<std::endl
<<"ba="<<(ba)<<std::endl
<<"a^b="<<(a^b)<<std::endl;
return 0;
}







md

Posted: Mon Aug 31, 2009 6:02 pm Post subject: Re: Write the source code 


saltpro15 @ 20090831, 8:57 am wrote: Just because I'm waiting for my pancakes to finish cooking, here's another version
c++: 
#include<cstdio>
#include<cmath>
double r, area;
main()
{
printf("Enter a radius greater than or equal to 0\n");
scanf("%f", &r); // scanf needs a pointer when inputting variables, hence &r instead of r
area= M_PI * (r*r);
printf("%.5f\n", area); // the .5 will print to 5 decimal places
}

That's C; using C++ links to C headers.
Also... I am moving this out of C++ Help, since obviously it has nothing to do with help 





saltpro15

Posted: Mon Aug 31, 2009 7:06 pm Post subject: RE:Write the source code 








md

Posted: Mon Aug 31, 2009 7:17 pm Post subject: RE:Write the source code 


Nein. "math.h" is the C math library  infact the exact same as cmath in most cases (sometimes some things are undefinded).
However, using the C math library is really the correct thing to do in this case  if you use it as "cmath". 





jhooper3581

Posted: Mon Aug 31, 2009 7:35 pm Post subject: (No subject) 


How do you guys use that type of code typing posting in this forum? (Colored texts, et cetra). 





DtY

Posted: Mon Aug 31, 2009 7:36 pm Post subject: Re: RE:Write the source code 


md @ Mon Aug 31, 2009 7:17 pm wrote: Nein. "math.h" is the C math library  infact the exact same as cmath in most cases (sometimes some things are undefinded).
However, using the C math library is really the correct thing to do in this case  if you use it as "cmath".
Does c++ have it's own math library? 





bbi5291

Posted: Mon Aug 31, 2009 8:24 pm Post subject: Re: Write the source code 


I guess there really was no reason to introduce a new math library in C++. You can't add templates, since the math functions are coded in assembly. (I suppose I/O does get a new library because there's much more room for flexibility) 





