C++ Height Calculation

[amaroa97]

Hello, I am new to c++ and I am trying to figure this out. Kindly help I will really appreciate it.


A small rocket is being designed to calculate the effect of wind shear in the vicinity of a thunderstorm. The designers predicted the performance of the rocket within this wind shear effect using the following formula ...

Height = 60 + 2.13t*2 - 0.0013t*4 + 0.000034t *4.751

(number after * is the exponent)
... where t is the elapsed time in seconds.

Write a C++ program that prompts the user for the elapsed time, computes the height (in feet) of the rocket for that given time, and outputs the height to the screen.

[amaroa97]

So far this is my code. Kindly help

#include <iostream>
#include <cmath>

using namespace std;

int main() {

// declare variables
float height, time;

//Ask for user input
cout<<"Enter time elapsed in seconds: ";

cin << time;
int a = 60;
double b = pow(2.13* time, 2);
double c = pow(0.0013* time,4);
double d = pow(0.000034* time,4.451);

// Calculate height
cout << height = a + b- c +d;
}

[48T7M4Gy]

#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    // declare variables
    double t = 0, height = 0;
    //Ask for user input
    cout<<"Enter time elapsed in seconds: ";
    cin >> t;
    
    //calculate height
    height = 60.0 + 2.13 *pow(t,2) - 0.0013*pow(t,4) + 0.000034*pow(t,4.751);
    
    cout << "time: " << t << " seconds\n";
    cout << "Height: " << height << " feet\n";
}

[mbozzi]

#include <iostream>
#include <cmath>

using namespace std; 

int main() {
  // declare variables near the first point-of-use.
  // use double consistently.

  cout<<"Enter time elapsed in seconds: ";
  // note the direction of the arrow >>
  double time; cin >> time;
  
  // variables whose values don't make sense to change later
  // should be marked const:
  double const a = 60.; 

  // Edit: precedence issues fixed (see below)
  double const b = 2.13 * pow(time, 2);
  double const c = 0.0013 * pow(time, 4);
  double const d = 0.000034 * pow(time, 4.451);
  double const height = a + b - c + d;

  cout << height << '\n';
}

[dhayden]

I think, you've gotten tripped up by precedence, in the formula
Height = 60 + 2.13t² - 0.0013t⁴ + 0.000034t^4.751,
2.13t² means 2.13(t²), not (2.13t)²

I'm an old guy who instinctively tries to save time when doing math calculations. You can compute t² faster by just multiplying it by itself. Ditto for t⁴. And t^4.751 is t⁴*t^0.751. So you can get away with just one call to pow:

#include <iostream>
#include <cmath>

using namespace std;

int
main()
{

    double height, time;

    cout << "Enter time elapsed in seconds: ";

    cin >> time;
    double t2 = time*time;      // t^2
    double t4 = t2*t2;          // t^4
    // height = 60 + 2.13t^2 - 0.0013t^4 + 0.00003t^4.751
    // calculate t^4.751 as t^4 * t^0.751
    height = 60 + 2.13*t2 - 0.0013*t4 + 0.00003*t4*pow(time,0.751);

    cout << height << '\n';
}

Enter time elapsed in seconds: 0
60

Hmm. That doesn't seem right. The rocket starts at a height of 60? Are you sure that formula is correct?

[mbozzi]

I think, you've gotten tripped up by precedence, in the formula

Whoops ;)
Thanks for the catch. I'll have to fix my response in a bit.

Edit:
fixed.

[amaroa97]

Thank you, everyone!