Why it isn't working? I have seen examples using this, but when I use it, it crashes. Why?(C) - c

Question

Why can't I do g->n=n ? Can someone explain?
#include <assert.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#define MAX 100000
int N[]={100,200,300,400,500,600,700,800,900,1000};
double B[]={0.125, 0.250, 0.375, 0.5, 0.625, 0.750, 0.875};
typedef struct Graph
{
int n;
int M[MAX][MAX];
int val;
int adjacent[MAX-1];
}G;
struct Graph * RandomDirectedGraph(int n, double b)
{
struct Graph * g = (struct Graph*)malloc(sizeof(struct Graph));
g->n=n;
int u,i,v;
for(u=0;u<n;u++)
{
for(i=0;i<n;i++)
{
g->M[u][i]=0;
}
}
int m=b*n*n;
for(i=0;i<m;i++)
{
do
{
u=rand()%n;
v=rand()%n;
}
while(u==v || g->M[u][v]==1);
g->M[u][v]=1;
}
};
int main()
{
int i,j,n,b;
for(i=0;i<sizeof(N)/sizeof(*N);i++)
{
for(j=0;j<sizeof(B)/sizeof(*B);j++)
{
RandomDirectedGraph(N[i],B[j]);
}
}
return 0;
}
When I compile and run it, ERROR pops up and says that some memory can't be written. I don't know what I'm doing wrong here.

Answer 1

The issue is that everytime you are executing the method RandomDirectedGraph, your application tries to reserve about 40GB of RAM memory. I guess your computer doesn't have that much.
Furthermore you should release all memory by calling free on the pointers.
For such big matrices, you don't use classic C matrices. You need external librarys for sparse matrix calculations like https://www.alglib.net/matrixops/sparse.php