Create 2D Array!

ajbharani · #1 08-Dec-2007, 06:47

hi

can we construct a 2Dimensional array with

int (*a)[10];

???????

thnx

davekw7x · #2 08-Dec-2007, 07:35

Quote:

Originally Posted by ajbharani

can we construct a 2Dimensional array...

In the first place, in C (and C++) there actually isn't any such thing as a 2-Dimensional array. We talk about such things, and there is notation for such things, but actually there are arrays (1-Dimensional). You can have an array of arrays and call it a 2-Dimensional array, (and we usually do).

Your statement declares that a is a pointer to an array of 10 ints.
If we want an array of arrays of 10 ints, then we could do something like the following

CPP / C++ / C Code:

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

int main()
{
    int n;

    int (*a)[10]; /* a pointer to an array of 10 ints */
    printf("sizeof(int)  = %d\n", sizeof(int));
    printf("sizeof(a[0]) = %d\n\n", sizeof(a[0]));

    printf("Enter a positive integer: ");
    if ((scanf("%d", &n) != 1) || (n < 1)) {
        printf("Invalid entry.\n");
        return 0;
    }
    printf("Allocating %d bytes for a.\n\n", n * sizeof(a[0]));
    a = malloc(n * sizeof(a[0]));
    if (a == NULL) {
        printf("malloc failed\n");
    }
    printf("Now you can access elements a[i][j] where\n");
    printf("  i is greater than or equal to zero and is less than %d\n", n);
    printf("  j is greater than or equal to zero and is less than 10\n\n");

    free(a);
    return 0;
}

Output:

Code:

sizeof(int)  = 4
sizeof(a[0]) = 40

Enter a positive integer: 3
Allocating 120 bytes for a:

Now you can access elements a[i][j] where
  i is greater than or equal to zero and is less than 3
  j is greater than or equal to zero and is less than 10

Regards,

Dave

ajbharani · #3 08-Dec-2007, 07:57

thnx..

wat is the diff in implementing a multi-dimensional array using
int *a[10] and int (*a)[10] ???

davekw7x · #4 08-Dec-2007, 10:55

Quote:

Originally Posted by ajbharani

...the diff...

The following statement declares a to be an array of 10 pointers to int

CPP / C++ / C Code:

int *a[10];

a[0] is a pointer to int
a[1] is a pointer to int
.
.
.
a[9] is a pointer to int

You can access a particular integer in the array by a[i][j] where
i is greater than or equal to zero and less than 10
and
j is greater than or equal to zero and less than however many ints for which you allocate storage and assigned the memory to a[i]

A 2-D array from this would involve allocating storage and assigning an address for each of the a[i]. You could consider that the array has 10 "rows," and each row can have as many ints as you allocate.

In the previous example, you end up with an array that has as many "rows" as you want (the value of n in the program), and each row has 10 ints.

So in the previous example
a[0] is a pointer to an array of 10 ints
a[1] is a pointer to an array of 10 ints.
.
.
a[n-1] is a pointer to an array of 10 ints.

You can access any integer by a[i][j] where
i is greater than or equal to zero and less than n
j is greater than or equal to zero and less than 10

Regards,

Dave

ajbharani · #5 09-Dec-2007, 20:28

nice piece of info . .
thnx

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Create 2D Array!

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