reading file, vector magnitude, angles

[texasz71]

so i have to write a program that reads x and y coordinates from a file, calculates vector lengths and positive radian and degree angles, and writes the data to a file which includes the x, y points plus the calculated data.

i get how to get the x and y coordinates from the file, but how do you plug those into finding the magnitude of the vector then finding the angles

here is what i have so far

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <cmath>

using namespace std;
double magnitude(double x, double y);
double angle(double x, double y);

int main()
{
double x=0,y=0;
ofstream datafile1(datafile1.dat);
datafile1 >> x >> y;

datafile1 << line;


}

[codewalker]

You need help with the formula or to convert the formula into c++ syntax?

[texasz71]

no i need to know how to take the x and y coordinates from the file and plug them into the magnitude formula. im thinkin i assign those a variable such as x = a, y= b?

[codewalker]

You are already taking the x, y from file. Just have another variable and assign the result of the formula to that variable.
Something like double result = x*y+ 2 (or whatever the formula is) and print the value.

[texasz71]

sweet thanks dude. ill have more questions later haha

[Chervil]

The code above doesn't compile, it can't be what was actually tried.
But it is attempting to both read and write from/ to an output file, which won't work, unless it is opened for input/output.

#include <iostream>
#include <fstream>

    using namespace std;

int main()
{
    double x = 1.2;
    double y = 3.4;

    // Write out the data
    ofstream datafile1("datafile1.dat");
    datafile1 << x << ' ' << y << endl;
    datafile1.close();

    // Read in the data
    x = 0;
    y = 0;
    ifstream datafile2("datafile1.dat");
    datafile2 >> x >> y;
    datafile2.close();

    // and display it
    cout << "x: " << x << "  y: " << y << endl;

}

[texasz71]

heres what i have so far. i know the bottom 1/3 is wrong...but any suggestions on what to change would be awesome

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <cmath>

using namespace std;
double vector(double x, double y);
double angle(double x, double y);

int main()
{
double x=0,y=0;
// Open the data file and read the text
ofstream datafile1("datafile1.dat");
datafile1 << x << " " << y;
datafile1.close(); // close data file


double vector;
double xv;
double yv;
xv = 0;
yv = 0;
double angle (double a, double b);
double sqrt (xv * xv + yv * yv);
double rad;
double deg;
rad = 0;
deg = 0;

// Print results
cout << sqrt << endl;
cout << 180 * rad / 3.14 << endl;
cout << 180 * deg / 3.14 << endl;


}

[Chervil]

I've absolutely no idea what it is you want to achieve.
This is your code...

// Open the data file and read the text
ofstream datafile1("datafile1.dat");
datafile1 << x << " " << y;
datafile1.close(); // close data file 

The comment says it is reading some text. But the actual code is writing out two values.

Which is it you are aiming to do?

[martianxx]

Do you understand how to work out the angle between two vectors/magnitude of a vector. You will need functions to get the magnitude, find the angle and work out the vector between the co ordinates you are reading in. This is what I made, your solution would be different to account of the reading/writing of your file:

#include <cmath>
#include <iostream>

#ifndef PI
#define PI 3.14159265
#endif

using std::cout;
using std::endl;

struct Vector{float i,j,k;}; //vector struct
struct Point{float x,y,z;}; //cord struct
//functions
float GetAngle(Vector v1, Vector v2, float *a, float *b);
float Magnitude(Vector v1);
Vector GetVec(Point a, Point b);

int main()
{
	//create two vectors to compare
	Vector myVec1 = {0};
	Vector myVec2 = {0};

	//create two sets of points (you would read them in)
	Point a1 = {1,5,-7};
	Point a2 = {-2,12,19};
	Point b1 = {12,-9,1};
	Point b2 = {0,-7,1};

	//find out the vectors between the points
	myVec1 = GetVec(a1,a2);
	myVec2 = GetVec(b1,b2);

	//create floats to hold the magnitudes of the two vectors
	float magnitude1 = 0.f;
	float magnitude2 = 0.f;

	//create variable to store the angle
	float angle = 0.f;
	//work out the angle
	angle = GetAngle(myVec1, myVec2, &magnitude1, &magnitude2);
	//output results (you would write this to your file)
	cout << angle << endl;
	cout << magnitude1 << endl;
	cout << magnitude2 << endl;
        
        return 0;

}

float GetAngle(Vector v1, Vector v2, float *a, float *b)
{
	float tempAngle;
	float DotProduct;

	//store the magnitude values via our pointers
	*a = Magnitude(v1);
	*b = Magnitude(v2);
	//work out the dot product of the two vectors
	DotProduct = ((v1.i * v2.i)+(v1.j*v2.j)+(v1.k * v2.k));
	//angle = inv cosine of dot product divided the the product of the magnitude of vector a and vector b
	tempAngle = acos(DotProduct/((*a) * (*b)));

	//return the angle in degrees
	return tempAngle*180/PI;
}
float Magnitude(Vector v1)
{
	return sqrt(pow(v1.i, 2) + pow(v1.j, 2) + pow(v1.k, 2)); //return the magnitude (pythagoras)
}
Vector GetVec(Point a, Point b)
{
	Vector temp = {0};

	temp.i = b.x - a.x;
	temp.j = b.y - a.y;
	temp.k = b.z - a.z;

	return temp; //return vector between two points
}

Hope this helps. If you decide to use this make sure you go through it and understand it.

[texasz71]

sorry guys...im pretty new at this still. thanks for writing your own code maritanxx, but i like to write my own, but i will be taking bits, pieces and suggestions from yours

thans for the help guys

[martianxx]

thats okay, its much better if you write your own code :) Hopefully mine can give you a starting point.