Question

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How to work with complex numbers in C?

So I have this piece of C code that compiles with errors saying that ‘complex’ does not name a type:

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

int main ()
{
    int B=9;
    double theta;

    double complex w;
    float x,y;

    x= 5*cos (theta) - 2;
    y= 5*sin (theta);


    double complex z=x+y*I;
    w=z+(B/z);

    for(theta=0;theta<=360;theta=+30)
    { printf ("%.2f  %.2f  %.2f  %.2f",creal(z), cimag(z),y,creal(w), cimag(w));
        printf ("/n");
    } 

    return 0;

    system ("pause");
}

I already include the <complex.h> so why is there still an error for the ‘complex’. There are also other errors, but let just focus on this one first.

Answer 1

Are you using GCC as your compiler? If yes, you need to enable C99 support by using the -std=c99 or -std=gnu99 compiler flag.

Also, declare variables before you use them. Here:

double complex z=x+y*I;

neither x nor y have been declared yet. Of course you also need to initialize them. For example:

float x = 5 * cos(theta) - 2;
float y = 5 * sin(theta);
double complex z = x + y * I;