first.c

#include <stdio.h>

struct vector3 {
    float x;
    float y;
    float z;
};

struct vector3 vector3_add(struct vector3 v0, struct vector3 v1) {
    struct vector3 new_vec;
    new_vec.x = v0.x + v1.x;
    new_vec.y = v0.y + v1.y;
    new_vec.z = v0.z + v1.z;

    return new_vec;
}

void vector3_init(struct vector3 *v0, float x, float y, float z) {
    v0->x = x;
    v0->y = y;
    v0->z = z;
}

int main(int argc, char **argv) {
    struct vector3 va;
    struct vector3 vb;
    struct vector3 vd;
    struct vector3 *vshit = &vd;

    vector3_init(&va, 1, 2, 3);
    vector3_init(&vb, 4, 5, 6);

    vector3_init(vshit, 4, 5, 6);

    struct vector3 vc = vector3_add(va, vb);

    printf("vector3 %f %f %f\n", vc.x, vc.y, vc.z);
    return 0;
}