Problems in passing 2-D array to a function

[boral]

I am learning to pass arrays to functions. My problem is this : I will scan a 2-D array in main() function. Pass the order n of the matrix and the address of first element to a function called pass(). Then I will print all the elements in pass().


I cannot understand what is wrong with my code. Please point out my mistake.

# include<stdio.h>


main()
{
	float a[50][50];
	int i, j, n ;
	void pass( int , float* ) ;
	printf("Enter n : ") ;
	scanf("%d", &n) ;


	for( i = 0; i < n ; i++)
	{
		for( j = 0; j < n ; j++)
		{
			printf("\n Enter a%d%d = ", i, j) ;
			scanf("%f", &a[i][j]) ;
		}
	}


	pass(n, &a[0][0]) ;
	
}


void pass( int n, float *a_pointer )
{
	int i, j ;
	for( i = 0; i < n ; i++)
	{
		for( j = 0; j < n ; j++)
		{
			printf("\n\n %f", *(a_pointer + n*i + j )) ;
		}
	}
}

[Click_here]

Because *a_pointer can only be used for a 1D array.

Here is a good link to get you started
23.1: Multidimensional Arrays and Functions

[CodeMonkey]

That is odd. If you can live with fixed N, types are your friend:

enum { N = 50 };

typedef struct {
    float data[N][N];
} Float2d;

void pass(const Float2d *grid)
{
    int i, j;
    for (i = 0; i < N; ++i)
        for (j = 0; j < N; ++j)
            printf("%f\n", grid->data[i][j]);
}

grid->data knows about the layout so you don't have to. Of course, fixed N is probably not acceptable.

[CodeMonkey]

Your 2d array a is layed out 50 x 50, not n x n. That's your problem. This might help you see it:

int main()
{
    float a[10][10] = {0};
    int i, j, n;

    printf("Enter n : ") ;
    scanf("%d", &n) ;
 
    for(i = 0; i < n ; i++)
    {
        for(j = 0; j < n ; j++)
        {
            printf("\n Enter a%d%d = ", i, j) ;
            scanf("%f", &a[i][j]) ;
        }
    }

    printf("\nMemory layout:\n");
    for( i = 0; i < n ; i++)
    {
        for( j = 0; j < n ; j++)
        {
            const float *p = &a[i][j];
            printf("i=%d j=%d p=%p floatsAway=%d\n", i, j, p, p - &a[0][0]);
        }
    }
}

Your code will work when n == 50.

[Aslaville]

for( j = 0; j < n ; j++)
        {
            printf("\n\n %f", *(a_pointer + n*i + j )) ; /* Here  */
        }
  
}

What exactly are you trying to do here? You have some out of bounds arrays access.

printf("\n\n %f", *(a_pointer + n*i + j ));
            /* for say [3][3]
            /* 1st loop -> 0 , 1 , 2
            /* 2rd loop -> 3 , 4 , 5
            */