I want to check if three sides of a triangle is a right angle using the Pythagoras theory by calling a function

Question

I want to call a function to calculate Pythagoras and to see whether it is true that a triangle is a right angled triangle using three inputs. I am very new to C++ and will appreciate help with this:

This is my code, it runs but does not work correctly:

    #include <iostream> 
#include <cmath> 

using namespace std;

double pythagorusTheorem(double a, double b, double c);

int main(){

double a;
double b;
double c;

cout << "Write the three sides of the triangle, enter biggest first and shorter sides after: " << endl;

cin >> a >> b >> c; 



if (double val=pythagorusTheorem(a,b,c) == true){

cout << "This is a right-angle triangle " << endl;

}

if (double val=pythagorusTheorem(a,b,c) == false) {

cout << "This is not a right angled triangle " << endl; 

}

return 0;
}


double pythagorusTheorem(double a, double b, double c){

a = pow(b,2) + pow(c,2);



}

What do you mean by this line `if (double val=pythagorusTheorem(a,b,c) == true)` ? — Naseef Chowdhury, Oct 22 '17 at 18:49
There are an infinite number of ways for something to not work correctly. Please be more specific. — Daniel H, Oct 22 '17 at 18:49
When I enter three input a, b and c it does not tell me whether is rightangled or not using the cout output — Jihjin Kairo Hunter, Oct 22 '17 at 18:50
I meant by the line "if (double val=pythagorusTheorem(a,b,c) == true) " if C^2 = a^2 + a^2 then it is a right angled triangle — Jihjin Kairo Hunter, Oct 22 '17 at 18:52
To prove Pythagorus Theorem, it can' be a = pow(b,2) + pow(c,2); you have to calculate the square root, as the theorem states a^2 = b^2 + c^2 where a is the hypothenuse. Also instead of two if, maybe you could use else? — Vega, Oct 22 '17 at 22:04

hnefatl · Answer 1 · 2017-10-22T19:03:17.120

1

You don't return a value from pythagorusTheorem. This is undefined behaviour. In addition:

if (double val=pythagorusTheorem(a,b,c) == true)

...reaaaally doesn't do what you expect. Remember that == is for comparing if two values are equal, but = is for assigning a value to a variable.

You'd be much better suited by changing the function to one which returns true or false depending on if your values fulfill the required condition:

bool pythagorasTheorem(double a, double b, double c)
{
    return a*a == b*b + c*c;
}

Then change your comparisons to:

if (pythagorasTheorem(a,b,c))
{
    cout << "This is a right-angle triangle " << endl;
}

I have to refer you to this lovely list of C++ books - you should read up on functions, in particular. This will likely also be helpful.

edited Oct 22 '17 at 19:03

answered Oct 22 '17 at 18:51

hnefatl

5,860
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Given this, you just need to say `if (pythagorusTheorem(a, b, c))`; you *almost never* need to compare to `true` or `false` explicitly. – Daniel H Oct 22 '17 at 18:53
1

@DanielH Caught me mid-edit, sorry... – hnefatl Oct 22 '17 at 18:54
Multiplication is more efficient than calling the `pow` function, so `a * a` would be more efficient than `pow(a, 2)`. – Thomas Matthews Oct 22 '17 at 19:01
@ThomasMatthews Yeah, I was trying to stay in the vein of the original code. I'll edit though, as I suppose I've ripped enough of OP's original code up anyway. – hnefatl Oct 22 '17 at 19:02

score 0 · Answer 2 · answered Oct 22 '17 at 19:42

0

If you write your function like this:

bool pythagorasTheorem(double a, double b, double c)
{
    a *= a;
    b *= b;
    c *= c;
    return a == b + c || b == c + a || c == a + b;
}

using @hnefatl solution, you don't have to enter longest side first

answered Oct 22 '17 at 19:42

Killzone Kid

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I want to check if three sides of a triangle is a right angle using the Pythagoras theory by calling a function

2 Answers2