structured_grids/cellular_automaton: fixed some warnings in C example

cellular_automaton/wireworld_c/configuration.c

@@ -2,6 +2,7 @@
 #include <mpi.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "configuration.h"
 

cellular_automaton/wireworld_c/main.c

@@ -67,7 +67,6 @@ void broadcast_configuration(conf_t *c) {
 
 void read_input(const conf_t *c, world_t *world) {
    int rank;
-   MPI_Comm cart_comm;
 
    char input_filename[FILE_NAME_SZ];
    MPI_File file;

cellular_automaton/wireworld_c/simulation.c

@@ -200,7 +200,7 @@ void do_simulation_persistent_request_no_overlap(world_t *world, size_t n_genera
    const size_t n_neighbors = world->transfer.n_neighbors;
    const size_t sz = world_get_storage_size(world);
 
-   size_t g, i;
+   size_t g;
    MPI_Request *requests = world->transfer.persistent_requests;
 
    for(g = 0; g < n_generations; g++) {
@@ -225,7 +225,7 @@ void do_simulation_persistent_request_overlap(world_t *world, size_t n_generatio
    const size_t n_neighbors = world->transfer.n_neighbors;
    const size_t sz = world_get_storage_size(world);
 
-   size_t g, i;
+   size_t g;
    MPI_Request *requests = world->transfer.persistent_requests;
 
    for(g = 0; g < n_generations; g++) {

cellular_automaton/wireworld_c/world.c

 #include <string.h>
+#include <stdlib.h>
 
 #include "world.h"
 
@@ -44,7 +45,6 @@ void world_init(world_t *world, size_t *global_size, const conf_t *c)
 {
    int dim, lo, hi;
    int nprocs[2], periods[2], proc_coord[2];
-   char *buffer;
    size_t storage_size;
    MPI_Comm cart_comm;