typedef struct graph *Graph;
Graph GRAPHinit(int);
struct graph{int V; int E; int **adj;}
 
int **MATRIXint(int r, int c, int val)
{ int i,j;
  int **t=malloc(r*sizeof(int *));
   if(t){ for(i=0; i<r; i++) 
              t[i]=malloc(c*sizeof(int)); if{t[i]}
                                                     {for(i=0;i<r; i++)
                                                       for(j=0;j<c;j++) t[i][j]=val;}
                                                    else{printf("mem allocation error.\n"); return 0;}
          }else{printf("mem allocation error.\n"); return 0;}
    return t;
}
 
Graph GRAPHinit(int V)
{ Graph G = malloc(sizeof*G);
   if(G){G->V=V; G->E=0; G->adj=MATRIXint(V,V,0);}
                  else{printf("mem allocation error.\n"); return 0;}
 return G;
}

free(G); G=NULL;

/* free rows made by MATRIXint() */
/* where V represents the rows */
for (i = V-1; i >= 0; i--) {
	if (G->adj[i] != NULL) {
		free(G->adj[i]);
		G->adj[i] = NULL;
	}
}

/* free 2-dimensional pointer */
if (G->adj != NULL) {
	free(G->adj)
	G->adj = NULL;
}

/* free Graph */
if (G != NULL) {
	free(G);
	G = NULL;
}

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

#define DATA 2

struct List {
	char **data;
};

struct Page {
	struct List *list;
};

int main() {
	/* local variables */
	int i, j, k;

	/* allocate memory; page */
	struct Page *page_1 = malloc(sizeof *page_1);
	if (page_1 == NULL) {
		fprintf(stderr, "page_1 allocation failed\n");
		return 0;
	}
	printf("page_1 allocated\n");

	/* allocate memory; list */
	page_1->list = malloc(sizeof *page_1->list);
	/* if allocation failed */
	if (page_1->list == NULL) {
		fprintf(stderr, "page_1->list allocation failed\nfree page_1\n");
		/* free memory; page */
		free(page_1);
		page_1 = NULL;
		return 0;
	}
	printf("page_1->list allocated\n");

	/* allocate memory; data */
	page_1->list->data = malloc(DATA * sizeof *page_1->list->data);
	/* if allocation failed */
	if (page_1->list->data == NULL) {
		fprintf(stderr, "page_1->list->data allocation failed\nfree page_1->list & page_1\n");
		/* free memory; list */
		free(page_1->list);
		page_1->list = NULL;
		/* free memory; page */
		free(page_1);
		page_1 = NULL;
	}
	printf("page_1->list->data allocated\n");

	/* allocate memory; data rows */
	for (i = 0; i < DATA; i++) {
		page_1->list->data[i] = malloc(10);
		/* allocation failed */
		if (page_1->list->data[i] == NULL) {
			fprintf(stderr, "page_1->list->data[%i] allocation failed\nfree page_1->data & page_1->list & page_1", i);
			/* free any memory done during the loop */
			for (k = i-1; k >= 0; k--) {
				/* free memory; data rows */
				free(page_1->list->data[k]);
				page_1->list->data[k] = NULL;
			}
			/* free memory; data */
			free(page_1->list->data);
			page_1->list->data = NULL;
			/* free memory; list */
			free(page_1->list);
			page_1->list = NULL;
			/* free memory; page */
			free(page_1);
			page_1 = NULL;
		}
		printf("page_1->list->data[%i] allocated\n", i);
	}

	/* free memory; data rows */
	for (j = DATA-1; j >= 0; j--) {
		if (page_1->list->data[j] != NULL) {
			free(page_1->list->data[j]);
			page_1->list->data[j] = NULL;
		}
		printf("page_1->list->data[%i] freed\n", j);
	}
	/* free memory; data */
	if (page_1->list->data != NULL) {
		free(page_1->list->data);
		page_1->list->data = NULL;
		printf("page_1->list->data freed\n");
	}
	/* free memory; list */
	if (page_1->list != NULL) {
		free(page_1->list);
		page_1->list = NULL;
		printf("page_1->list freed\n");
	}
	/* free memory; page */
	if (page_1 != NULL) {
		free(page_1);
		page_1 = NULL;
		printf("page_1 freed\n");
	}

	return 0;
}