Matrix multiplication of a vertex of a cube.

mathrix.c

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

#define _USE_MATH_DEFINES

struct vector {
   double x, z, y;
};

struct vector *rot_x(const struct vector *_matrix, const double d_angle){
   //printf("sizeof _matrix: %ld\n", sizeof(*_matrix));
   struct vector *_object = malloc(sizeof(struct vector)*sizeof(*_matrix));
   if (_object == NULL) {
      fprintf(stderr, "couldn't allocate enough space\n");
      exit(1);
   }

   for (int i = 0; i < (int)sizeof(*_matrix)/3; i++){
      _object[i].x = _matrix[i].x;
      _object[i].y = (_matrix[i].y*cos(d_angle*M_PI/180.0))+(-_matrix[i].z*sin(d_angle*M_PI/180.0));
      _object[i].z = (_matrix[i].y*sin(d_angle*M_PI/180.0))+(_matrix[i].z*cos(d_angle*M_PI/180.0));
   }

   return _object;
}

struct vector *rot_z(const struct vector *_matrix, const double d_angle){
   struct vector *_object = malloc(sizeof(struct vector)*sizeof(*_matrix));
   if (_object == NULL) {
      fprintf(stderr, "couldn't allocate enough space\n");
      exit(1);
   }

   for (int i = 0; i < (int)(sizeof(*_matrix))/3; i++){
      _object[i].x = (_matrix[i].x*cos(d_angle*M_PI/180.0))+(-_matrix[i].z*sin(d_angle*M_PI/180.0));
      _object[i].y = (_matrix[i].x*sin(d_angle*M_PI/180.0))+(_matrix[i].z*cos(d_angle*M_PI/180.0));
      _object[i].z = _matrix[i].z;
   }
   return _object;
}
int print_transformation(const struct vector *_matrix){
   for (int i = 0; i < sizeof(*_matrix)/3; i++)
      printf("%10.4f ", _matrix[i].x);

   putchar('\n');

   for (int i = 0; i < sizeof(*_matrix)/3; i++)
      printf("%10.4f ", _matrix[i].y);

   putchar('\n');

   for (int i = 0; i < sizeof(*_matrix)/3; i++)
      printf("%10.4f ", _matrix[i].z);

   putchar('\n');

   return 0;
}

int main(int argc, char *argv[]){
   if (argc != 2) return 1;
   const struct vector cube[8] = {
      {8.0,  0.0, 5.0},  // vertex A
      {8.0,  2.0, 5.0},  // vertex B
      {-8.0, 2.0, 5.0},  // vertex C
      {-8.0, 0.0, 5.0},  // vertex D
      {8.0,  0.0, 8.0},  // vertex E
      {8.0,  2.0, 8.0},  // vertex F
      {-8.0, 2.0, 8.0},  // vertex G
      {-8.0, 0.0, 8.0}   // vertex H

   };

   struct vector *rot_x_cube;
   int d_eye = atoi(argv[1]);
/*
   puts("Before transformation:");
   print_transformation(cube);

   putchar('\n');

   puts("After transformation: ");
   print_transformation(rot_y_cube);
*/

/*
   for (int i = 0; i < sizeof(cube)/3)

   free(rot_y_cube);
   for (int i = 0; i < sizeof(cube)/3; i++)
      printf("%d ", closes_x[i]);
   putchar('\n');
   for (int i = 0; i < sizeof(cube)/3; i++)
      printf("%d ", closes_y[i]);
*/
   for (int i = 0; i < 120; i++){
      char execute[500];
      rot_x_cube = rot_z(cube, (double) (i*90/120));
      FILE *fp = fopen("file.dat", "w");
      if (fp == NULL){
         fprintf(stderr, "couldn't open file.dat\n");
         exit(1);
      }

      for (int c = 0; c < (int) (sizeof(cube)/(sizeof(double)*3)); c++){
         fprintf(fp, "0 0 %10f %10f\n", rot_x_cube[c].x/rot_x_cube[c].y, rot_x_cube[c].z/rot_x_cube[c].y);
      }

      fclose(fp);
      sprintf(execute, "gnuplot -e \"set terminal png; plot [-5:5] [0:10]\'file.dat\' using 1:2:3:4 with vectors\" > \"/mnt/c/Users/User/Desktop/ffd/plot-%d.png\"\n", i);
      printf(execute);
      system(execute);
      free(rot_x_cube);

   }
   /*
   printf("length of cube %ld %d\n", sizeof(cube), (sizeof(cube)/3));
   for (int i = 0; i < (int )(sizeof(cube)/(sizeof(double)*3)); i++){
      printf("0 0 %10f %10f\n", rot_y_cube[i].x, rot_y_cube[i].y);

   }
   */
   return 0;

}