cast to pointer from integer of different size

#include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
 #include <sys/time.h>
 #include <pthread.h>
 
 #define NTHREADS 4
 
 int dim ;
 pthread_mutex_t m; /* Mutex protecting the sum value */
 pthread_t thread_id[NTHREADS]; /* Thread ids */
 float **A, **B, **C;
 
 void *prod (void *s){
  int *id=(int *)s;
  int idd=*id;
 
 
  /* Define local variables */
  int i,j,k, start, end, len ;
  float **Aa, **Bb, **Cc;
 
  start = dim*idd; /* Start of this threads slice of the vectors */
  end = start + dim; /* End of the slice */
 
 
  for (i = 0 ; i < dim; i++)
  {
  for (j = 0; j < dim; j++)
  {
  Cc[i][j] = 0;
  for (i=start; i<end ; i++) {
 
  Cc[i][j] += Aa[i][k] * Bb[k][j];
  }
  }
  }
  pthread_mutex_lock (&m); /* Lock the mutex */
  C[i][j] += Cc[i][j]; /* Update the shared variable */
  pthread_mutex_unlock (&m); /* Unlock the mutex */
 
  pthread_exit(NULL); /* Done! */
 }
 
 int main ( int argc, char *argv[] )
 {
  void *status;
  float **A, **B, **C;
  int i,j,k;
 
  if ( argc == 2)
  dim = atoi(argv[1]); // get the dimension of the matrix
  // from the command prompt
 
  else
  dim = 128;
 
 
 
  A = (float **)malloc(sizeof(float*)*dim);
  B = (float **)malloc(sizeof(float*)*dim);
  C = (float **)malloc(sizeof(float*)*dim);
 
  for (i = 0 ; i < dim; i++)
  {
  A[i] = (float *)malloc(sizeof(float)*dim);
  B[i] = (float *)malloc(sizeof(float)*dim);
  C[i] = (float *)malloc(sizeof(float)*dim);
  }
 
  for (i=0; i<dim; i++)
  {
  for (j = 0 ; j < dim; j++)
  {
  A[i][j]=rand();
  B[i][j]=rand();
  }
  }
 
  struct timeval t1, t2;
  gettimeofday(&t1, NULL);
 
  // you need to parallelize this
  // perform the multiplication
  for(i=0;i<NTHREADS;i++) {
 
  pthread_create(&thread_id[i], NULL, prod, (void *)i);
  }
  /* Wait on the other threads */
  for(i=0;i<NTHREADS;i++) {
  pthread_join(thread_id[i], &status);
  }
 
  gettimeofday(&t2, NULL);
 
  double t = (t2.tv_sec - t1.tv_sec) + (t2.tv_usec - t1.tv_usec ) / 1000000.0;
  // take the difference and report it in seconds
  printf("execution time %f seconds\n",t);
 }

pthread_create(&thread_id[i], NULL, prod, (void *)i);