Question

I’m trying to make an array of structs where each struct represents a celestial body.

I don’t have that much experience with structs, which is why I decided to try to use them instead of a whole bunch of arrays. However, I keep on running into numerous different errors. I’ve tried to implement the techniques that I’ve seen on various threads and on Stack Overflow (such as Array of structs in C and Initialize array of structs in C), however not all of them were applicable.

Further information for those who have read this far: I don’t need any of this to be dynamic, I know/define the size of everything beforehand. I also need this to be a global array as I’m accessing this in several different methods which have defined arguments (i.e., GLUT methods).

This is how I’m defining the struct in my header:

struct body
{
    double p[3]; // Position
    double v[3]; // Velocity
    double a[3]; // Acceleration
    double radius;
    double mass;
};

I have a list of other global variables that I’m defining before I define the interior of the struct, and one of those is the array of this struct (basically, if I’m being too unclear in my fogged speak, the line below is above the stuff above):

struct body bodies[n];

Just so you know, n is something that I’ve legitimately defined (i.e. #define n 1).

I use this array in several different methods, but the easiest and least space consuming one is a simplified form of my main. Here I initialize all of the variables in each of the structs, just to set the variables for certain before I modify them in some way:

int a, b;
for(a = 0; a < n; a++)
{
    for(b = 0; b < 3; b++)
    {
        bodies[a].p[b] = 0;
        bodies[a].v[b] = 0;
        bodies[a].a[b] = 0;
    }
    bodies[a].mass = 0;
    bodies[a].radius = 1.0;
}

The current error that I’m facing is nbody.c:32:13: error: array type has incomplete element type where line 32 is where I’m making the array of the structs.

One last clarification: By header I mean the space above int main(void), but in the same *.c file.

Answer 1

Use:

#include<stdio.h>

#define n 3

struct body
{
    double p[3]; // Position
    double v[3]; // Velocity
    double a[3]; // Acceleration
    double radius;
    double mass;
};

struct body bodies[n];

int main()
{
    int a, b;
    for(a = 0; a < n; a++)
    {
        for(b = 0; b < 3; b++)
        {
            bodies[a].p[b] = 0;
            bodies[a].v[b] = 0;
            bodies[a].a[b] = 0;
        }
        bodies[a].mass = 0;
        bodies[a].radius = 1.0;
    }

    return 0;
}

This works fine. Your question was not very clear by the way, so match the layout of your source code with the above.