Checking loop validity without using if statement - c++

Question

My lab professor wants us to use a while statement to have a parabola curving downward (gravity equation), but not going negative without an if statement in c++11. The code below works fine except for the fact that one negative value is still used. Is there a way to remove this last x/y value?
#include <iostream>
#include <cmath>
using namespace std;
int main() {
const double gravAccel = 9.82;
double initHeight;
double itemAngle;
double itemSpeed;
double horzCoord = 0;
double vertCoord;
cout <<"What is the initial height of the projectile?";
cin >> initHeight;
cout <<"What angle is the projectile launched at?";
cin >> itemAngle;
cout <<"What is the projectile's speed?";
cin >> itemSpeed;
while (vertCoord >= 0)
{
vertCoord = initHeight + horzCoord*tan(itemAngle) - ((gravAccel*pow(horzCoord,2))/(2*(pow(itemSpeed*cos(itemAngle),2))));
cout << horzCoord << "meters, " << vertCoord << "meters" << endl;
horzCoord++;
}
return 0; }

Answer 1

use a while statement to have a parabola curving downward (gravity equation), but not going negative without an if statement in c++11
Not really elegant, but you can embed the vertCord assignment in the while() test
while ( (vertCoord = initHeight + horzCoord*tan(itemAngle)
- ((gravAccel*pow(horzCoord,2))/(2*(pow(itemSpeed*cos(itemAngle),2))))) >= 0 )
{
cout << horzCoord << "meters, " << vertCoord << "meters" << endl;
horzCoord++;
}
Off Topic: as far I know, g (gravAccel) isn't 9.82 (m/s^2) but 9.807.

Answer 2

Gravity is approx. 9.81m/(s^2).
It doesn't seem like you are calculating the distance vertically and horizontally correct..
sin/cos/tan in C++ uses radians for the angle parameter.
++ operator on a double is going to increase it by 1.0.
If you want it to never be below zero, why not clamp it to its time? By that I mean calculate the time it takes for the projectile to hit the floor. Then loop for (time - currentTime) with some step while printing the X and Y coordinates of the projectile. This will make sure the vertical coordinate is always > 0.
#include <iostream>
#include <cmath>
using namespace std;
double calculateHorizontalCoordinate(double time, double initial_velocity, double initial_angle)
{
double initial_velocity_x = initial_velocity * cos(initial_angle * M_PI / 180.0);
return initial_velocity_x * time;
}
double calculateVerticalCoordinate(double time, double initial_velocity, double initial_angle)
{
double initial_velocity_y = initial_velocity * sin(initial_angle * M_PI / 180.0);
return (initial_velocity_y * time) - (0.5 * 9.81 * (time * time));
}
double calculateTime(double initial_velocity, double initial_angle)
{
double initial_velocity_y = initial_velocity * sin(initial_angle * M_PI / 180.0);
double time = (2 * initial_velocity_y) / 9.81;
return time;
}
int main() {
double initial_height = 0.0;
double initial_angle = 0.0;
double initial_velocity = 0.0;
double horzCoord = 0.0;
double vertCoord = 0.0;
cout <<"What is the initial height of the projectile?";
cin >> initial_height;
cout <<"What angle is the projectile launched at?";
cin >> initial_angle;
cout <<"What is the projectile's speed?";
cin >> initial_velocity;
double currentTime = 0.0;
double time = calculateTime(initial_velocity, initial_angle);
double step = time / 10.0;
while (time - currentTime >= numeric_limits<double>::min())
{
horzCoord = calculateHorizontalCoordinate(currentTime, initial_velocity, initial_angle);
vertCoord = calculateVerticalCoordinate(currentTime, initial_velocity, initial_angle);
cout << horzCoord << " meters, " << vertCoord << " meters" << endl;
currentTime += step;
}
return 0;
}
Input:
What is the initial height of the projectile? 0
What angle is the projectile launched at? 45
What is the projectile's speed? 25
0 meters, 0 meters
6.37105 meters, 5.73394 meters
12.7421 meters, 10.1937 meters
19.1131 meters, 13.3792 meters
25.4842 meters, 15.2905 meters
31.8552 meters, 15.9276 meters
38.2263 meters, 15.2905 meters
44.5973 meters, 13.3792 meters
50.9684 meters, 10.1937 meters
57.3394 meters, 5.73394 meters
Program ended with exit code: 0