C++ Calculating a triangle's angles given side lengths.

[Adam Cox]

Hi,

I'm working on my first C++ project for my college CPA course. So far we've only had a small handful of classes, and I'm stuck.

The program requires the user to enter 2 side lengths for a right angle triangle. From there we have to calculate the hypotenuse and the remaining 2 angles of the triangle.

So far I have user input being taken and the hypotenuse being calculated. The part I'm stuck on is calculating the remaining 2 angles. I've refreshed my memory on how to do this on paper like I did back in high-school math class, but I can't seem to program it if my life depended on it. So far I've spent 2 hours trying to figure this out and I've gone to at least a dozen websites to try to find code that I can cannibalize, but I haven't had any luck...

Can someone help me out please?

Here's what I have so far:

// Project 0 - Triangle
// Calculates the hypotenuse and angles of a right triangle.
// This program prompts the user for 2 values (mm, cm, m, km) -- Units of measure will be added later.
#include <iostream>
#include <string>
#include <cmath>
#include <stdio.h>
#include <math.h>	// do I need all of these #includes'?
using namespace std;

#define PI 3.14159265

int main()
{
	double xLength;
	double yLength;
	double zLength;
	double aAngle;
	double bAngle;
	double cAngle = 90;

	// Draw a pretty picture (helps the user to better understand what they are entering)
	cout << "  |* ";
	cout << "\n  |   * ";
	cout << "\n  | B    *       Z";
	cout << "\n  |         * ";
	cout << "\nX |            * ";
	cout << "\n  |               * ";
	cout << "\n  | 90           A   * ";
	cout << "\n  |_____________________* ";
	cout << "\n             Y \n\n";

	// Prompt the user.
	std::cout << "Enter the length of the two sides adjacent to the right angle. Include units of measure. (mm, cm, m, km)" << endl;
				// Units of measure will be added later.

	// Get side lengths
	// Get the Length of "x".
	cout << "x = ";
	cin >> xLength;
	cout << "You entered " << xLength << "." << endl;
	// Get the Length of "y".
	cout << "y = ";
	cin >> yLength;
	cout << "You entered " << yLength << "." << endl;

	// Calculate the Hypotenuse
	zLength = sqrt( xLength * xLength + yLength*yLength );
	cout << "Hypotenuse = " << zLength << endl;


	// Calculate angles
	// Calculate Anlgle 'a'

//	cout << "The angle of angle 'a' is: " << aAngle << endl;

	// Calculate angle 'b'



	return 0;
}

Thanks in advance to anyone who can help. I really appreciate it!

[BardaTheHobo]

You can try this for getting degree output

#define DEGTORAD(D)((D * PI) / 180.0) // Converts Degrees to radians
#define RADTODEG(R)((180.0 * R) / PI)//Converts Radians to Degrees 

Below should get the angles, I used your already labled sides and angles of ABC XYZ, the lowercase xyz was added by me, I took this out of a triangle calculator I made a long time ago so it should work

double x,y,z;
//Angle A
   y = X / Z;
   x = asin(y);
   z = RADTODEG (x);
    
 A = z;              

//Angle B
   y = Y / Z;
   x = asin(y);
   z = RADTODEG (x);
    
 B = z;
              

[Adam Cox]

Thanks, but how would I calculate what angle 'A' and angle 'B' are?

[cPlusN00b]

cmath includes the functions sin() and cos(), which you'll be needing for this program.. How's your trigonometry skills? Do ya know how to do the math?

[cPlusN00b]

Only thing is, cos() and sin() return angles in radians. You'll want to use something like Barda suggests ^ to convert the angle to degrees.

[Adam Cox]

I can kinda do trig on paper like what was learned in high-school math class, however it's been a few years and I can't seem to figure out how to code it. I did mess around with the sin() and cos() in my struggles, however I had no luck. All the numbers I got were negative or way to high to be correct...

[cPlusN00b]

yeah check out barda's edit ^
function you need is arc sine: asin();
if you know your trigonometric ratios, just plug in the sides you need

e.g.

float angle_a, opposite, hypoteneuse;
angle_a = asin(opposite / hypoteneuse);

once again, this will return radians not degrees.. you do the math :p

[Adam Cox]

Thanks guys, that worked great!