Keep getting zero

[Shrk]

Hey hey the answer iam am suppsoed to output is 4... but it seems no matter what i keep getting 0? any ideas?


#pragma intrinsic(sqrt, pow)
#include <iostream>
#include <math.h>
#include <cmath>
#include <iomanip>

using namespace std;

const float G = 6.674e-011;//0.00000000006674;
const float M = 5.974e+024;//5974000000000000000000000.0;
float g1 = 9.803;
float g2 = 9.792;
float height = 0.0;

float calculateHeight(const float G, const float M, float g1, float g2)
{
float height = 0.0;

height = sqrt(G*M)*((pow(1/g2,1/2))-(pow(1/g1,1/2)));
return height;
}

int main ()
{
height = calculateHeight(G, M, g1, g2);
cout << setprecision(30);
cout << "The Balloon is " << height << " meters High in the sky!" << endl;
system("pause");
return 0;
}

[Moschops]

Try this code and see if you can work it out. This is the beginning of learning to debug, so that you can work these things out for yourself.

#include <iostream>
#include <math.h>
#include <cmath>
#include <iomanip>

using namespace std;

const float G = 6.674e-011;//0.00000000006674;
const float M = 5.974e+024;//5974000000000000000000000.0;
float g1 = 9.803;
float g2 = 9.792;
float height = 0.0;

float calculateHeight(const float G, const float M, float g1, float g2)
{
float height = 0.0;

 cout << "sqrt(G*M) = " << sqrt(G*M) << endl;
 cout << "pow(1/g2,1/2) = " << pow(1/g2,1/2) << endl;
cout << "pow(1/g1,1/2) = " << pow(1/g1,1/2) << endl;

height = sqrt(G*M)*((pow(1/g2,1/2))-(pow(1/g1,1/2)));
 cout << "h1 = " << height << endl;
return height;
}

int main ()
{
height = calculateHeight(G, M, g1, g2);
cout << setprecision(30);
cout << "The Balloon is " << height << " meters High in the sky!" << endl;
system("pause");
return 0;
}

[Shrk]

Ah yeah that really shows what values are popping out. they keep equaling 1 and subtracting to zero. Why is that? Or is that... the answer?

[Shrk]

I tried putting that Setprecision in there. Cause i believe it rounds it to 1

[Moschops]

Don't include both math.h and cmath.

cmath is the C++ version of math.h, improved to be proper C++. Including both is insanity.

Try the sqrt function instead of pow to the half. You'll get closer...

[zwA4jE8b]

your variables are global, so there is no need to pass them in the function.

you should declare them in main.

[Moschops]

Try this :)

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

using namespace std;

const float G = 6.674e-011;//0.00000000006674;
const float M = 5.974e+024;//5974000000000000000000000.0;
float g1 = 9.803;
float g2 = 9.792;


float calculateHeight(const float G, const float M, float g1, float g2)
{
  float height = 0.0;


 float a,b,c,d,e;
 a = sqrt(G*M);
 b = sqrt(1/g2);
 c=  sqrt(1/g1);
 d = b - c;
 e = a*d;

 cout << "sqrt(G*M) = " << a << endl;
 cout << "sqrt(1/g2) = " << b << endl;
cout << "sqrt(1/g1) " << c << endl;

 
 height = a * d;
float h2 = sqrt(G*M)*((pow(1/g2,1/2))-(pow(1/g1,1/2)));
cout << "height = " << e << endl;
cout << "Calc all at once = " << h2 << endl;
return e;
}

int main ()
{
  float height;
height = calculateHeight(G, M, g1, g2);
cout << setprecision(30);
cout << "The Balloon is " << height << " meters High in the sky!" << endl;

return 0;
}

Then go and read about how computers actually store numbers.

[Duthomhas]

This is a common, and non-obvious problem for new programmers, particularly in C languages.

The following expressions are different:

double a = 1 / 2;
double b = 1.0 / 2;

The first line assignes the integer value "0" to the variable a.
The second line assignes the floating-point value "0.5" to the variable b.

If you only have integers on both sides of the / operator then it is an integer divide -- producing an integer result and discarding any remainder.

If you have a floating point value on at least one side of the / operator then you get a floating-point division -- producing a floating point result.

Hope this helps.

[Disch]

note:

((pow(1/g2,1/2))

1/2 is integral division. In C++, 1/2 will get you 0

Anything to the power of 0 is 1

Therefore:

// this line:
float h2 = sqrt(G*M)*((pow(1/g2,1/2))-(pow(1/g1,1/2)));

//reduces to this:
float h2 = sqrt(G*M)*((pow(1/g2,0))-(pow(1/g1,0)));

// reduces to this:
float h2 = sqrt(G*M)*(1-1);

// reduces to this:
float h2 = sqrt(G*M)*(0);

// reduces to this:
float h2 = 0;

That's why you get 0 every time.

Solutions would be to use sqrt() instead of pow, or use 0.5 instead of 1/2

[Shrk]

Sorry I have not replied ealier. Thanks for the responds. Yes i am new to this as you can see. I will try these out.