Sum of complex numbers expressed in polar form

Question

I need to sum two complex numbers (c1,c2) and then express the result in its polar form.

I don't really know how to access the result for c1+c2, I mean I store them in the variable "result" but when I try to access them I find myself in the ComplexPolar structure and so I can't access the result.real and result.img to calculate magnitude and angle:

#include<stdio.h>
#include<stdlib.h>
#include<math.h>

struct ComplexCartesian
{
    float real;
    float img;
};

struct ComplexPolar
{
    float magnitude;
    float angle;
};

struct ComplexPolar add_two_complex(struct ComplexCartesian c1, struct ComplexCartesian c2, struct ComplexPolar result)
{
    result.real= c1.real+c2.real;
    result.img=c1.img+c2.img;

    result.magnitude= sqrt((result.real)^2 + (result.img)^2);
    result.angle= atan2(result.img, result.real);
}

see [Why is my power operator (^) not working?](https://stackoverflow.com/q/4843304/995714). Please don't write code by assuming the syntax meanings. [Read a good tutorial first](https://stackoverflow.com/q/562303/995714). Note that C99 also has [built-in complex types](https://en.cppreference.com/w/c/numeric/complex) — phuclv, Mar 20 '21 at 01:27
Does this answer your question? [Why is my power operator (^) not working?](https://stackoverflow.com/questions/4843304/why-is-my-power-operator-not-working) — phuclv, Mar 20 '21 at 01:28

score 1 · Accepted Answer · edited Mar 19 '21 at 22:13

^2 is not how you square in C, you have to either multiply the number by itself or use libc pow function.

^2 is a XOR operation where you aim to toggle the second bit, but in your case you are using it on a float which violates the strict aliasing rule and cause undefined behavior (on top of not being what you seek).

See the code below with some comments:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

struct ComplexCartesian
{
    float real;
    float img;
};

struct ComplexPolar
{
    float magnitude;
    float angle;
};

struct ComplexPolar polar_from_cartesian_sum(struct ComplexCartesian c1, struct ComplexCartesian c2)
{
    struct ComplexPolar complexPolar; // here you declare the variable of your ComplexPolar struct

    c1.real += c2.real; // you don't need to have a result var, you can just reuse c1.
    c1.img += c2.img;
    complexPolar.magnitude = sqrt(c1.real * c1.real + c1.img * c1.img);
    complexPolar.angle = atan2(c1.img, c1.real);

    return complexPolar; // you return the value;
}


int main(void) {
    struct ComplexCartesian c1 = {0.12f, 0.15f};
    struct ComplexCartesian c2 = {0.42f, 1.15f};
    struct ComplexPolar complexPolar = polar_from_cartesian_sum(c1, c2);

    printf("%f %f\n", complexPolar.magnitude, complexPolar.angle);

    return 0;
}

Compile with gcc complex.c -lm && ./a.out

Output:

1.407693 1.177098

NB: Perhaps you should explicitly tell that your angle is expressed in radians, and also rename your function as polar_from_cartesian_sum

Radius = 1.41
θ = 67.44o = 1.18 radians

"^2 is not possible in C" -- It's actually _worse_ than not being possible. `^ 2` is legal — it computes the bitwise XOR with `2`. That means it'll compile just fine without warning, but fail in ways that are hard to understand. — Sam Henke, Mar 19 '21 at 06:49
@SamHenke actually I would like to give +15 to your comment. — linuxfan says Reinstate Monica, Mar 19 '21 at 10:19
Thank you so much, I was able to apply it and it finally worked, thanks! — Alex Rey, Mar 19 '21 at 19:28
You're welcome, glad it was helpful! @SamHenke excellent point, see my edit ;) — Antonin GAVREL, Mar 19 '21 at 22:04

Sum of complex numbers expressed in polar form

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