pointer to pointer inaccuracies - c

Question

I was working with 2D arrays, and tried passing it from one function to another. I've seen all the answers in here regarding that, and none of them seem to answer this particular type of problem. Its a simple thing I'm trying to achieve, but the answer is weird.
Here's the main():
int main(void)
{
int i=0,j=0,n=0,n2=0;
double **a, **a1, b=0;
printf("Enter 'n2' :");
scanf("%d", &n2);
a= makearray(n2);
for(i=0; i < n2; i++){
for(j=0; j < n2; j++){
a[i][j] = j;
printf("%.f ",a[i][j]);
}
printf("\n");
}
printf("\n\n\n");
for(i=0; i < n2; i++){ // print a
for(j=0; j < n2; j++){
b = a[i][j];
printf("%.f ", b);
}
printf("\n");
}
printf("\n\n\n");
return 0;
}
The function makearray() just returns a pointer to a pointer for the 2D array of size passed as an argument.
makearray() is:
double** makearray(int n2)
{
int i=0;
double** a;
a = malloc(n2 * sizeof(int *));
if(a == NULL){
fprintf(stderr, "out of memory\n");
exit(0);
}
for(i = 0; i < n2; i++){
a[i] = malloc(n2 * sizeof(int));
if(a[i] == NULL){
fprintf(stderr, "out of memory\n");
exit(0);
}
}
return a;
}
You can input 'n2', where (n2 x n2) becomes the matrix size , and with n=9, the output is:
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 0 1 2
0 1 2 3 4 5 6 7 8
I've not modified the first array in any way, just printed it again, any ideas why those two are different?

Answer 1

In your makearray, the malloc is using sizeof(int), but you're creating an array for doubles. Ints typically use 4 bytes, but doubles use 8 bytes. So you aren't malloc-ing enough memory for a 2-d array of doubles.

Answer 2

Try:
double** makearray(int n2)
{
int i=0;
double** a;
a = malloc(n2 * sizeof(double *)); //<- was sizeof(int *)
if(a == NULL){
fprintf(stderr, "out of memory\n");
exit(0);
}
for(i = 0; i < n2; i++){
a[i] = malloc(n2 * sizeof(double)); //<- was sizeof(int)
if(a[i] == NULL){
fprintf(stderr, "out of memory\n");
exit(0);
}
}
return a;
}