Thread: array help please

I'm trying to sum the elements in a 2D array but I keep getting errors. and I can't figure out what it is. Help would be appreciated, Thanks.

Code:

#include <stdio.h>
#define MAXROW 10
#define MAXCOL 10

int matrix[MAXROW][MAXCOL]={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20},row,col;

int addition(int matrix[MAXROW][MAXCOL],int i,int j);
int main(void)
	{
	addition(matrix[MAXROW][MAXCOL],row,col);
	return 0
	}

int addition(int matrix[MAXROW][MAXCOL],int i,int j)
	{
	for (i=0;i<MAXROW;++i)
		for (j=0;J<MAXCOL;++j);
			sum+=matrix[i][j];
	printf("\nsum=%d",sum);
	return 0
	}

int matrix[MAXROW][MAXCOL]={1,2,3,4,5,6,7,8,9,10,11,12
,13,14,15,16,17,18,19,20}

That is not the correct way to initialize a two dimensional array. You want:

Code:

signed int array[3][3] = 
{
    { 1, 2, 3 },
    { 4, 5, 6 },
    { 7, 8, 9 }
};

Consider a multiple deminsion array as an array of arrays (of arrays of ... ). Thus, you have an array of arrays of integers. As such, you should be initializing each array in turn, as per above. It's the RightThing(TM) to do.

Here is a problem:

for (j=0;J<MAXCOL;++j);

Your loop in effect does nothing at all because you're telling it not to by having that semi-colon there.

It's always the little things.


On a side note, your array has a total of 100 cells, not 20 as it appears you think it does.

The size of the array is: dimension1_size * dimension2_size * ...


Quzah.

Originally posted by CXHatchback
And according to my C book, with the values i entered, it should be a 2x10 array

The array size is as you declared it. It's 10 by 10. The values you've entered will fill the first twenty elemets.

Either way is supported by the standard. It's usually best to use the method I described for readability. You'll definately want to use this method if you start using more dimensions than 2.

Quzah.

Originally posted by CXHatchback
I keep getting an error that says illegal implicit conversion from 'int' to 'int[*][10]' and I have no idea what that means

The program stops where i try to call the addition function from the main

You are calling the function incorrectly:

addition(matrix[MAXROW][MAXCOL],row,col);

Should be:

addition( matrix, row, col );

Otherwise what you're doing is passing it matrix[10][10], which is outside of the bounds of the array itself.

Quzah.

There is a difference between a function prototype / definition and the actual call of it. This is especially true when using pointers and arrays.

Code:

void function( int );   /* A prototype. */

Here we've prototyped a function that will take an integer, and will return void.

When we create the function itself, we actually have to name the variable so we can use it in the fuction. In the prototype, you can omit names, or include names if you wish for the variables.

Prototypes are optional. Definitions are not.

The function definition:

Code:

void function( int myint )
{
    printf("This is myint: %d.\n", myint );
}

Now with arrays, it gets trickier.

void myfun( int array[] ); /* valid */
void myfun( int array[SIZE] ); /* valid */
void myfun( int array[][SIZE] ); /* valid */
void myfun( int array[SIZE][SIZE] ); /* valid */
void myfun( int array[SIZE][] ); /* invalid */

The final one is invalid, because you must specify the last dimension size in a multi-dimension array.

In any case, when you're passing an entire array to a function that accepts an array, you only ever pass it the name. (Or a spot in the array for trickier stuff, but basicly ignore that for now.)

There's more to it, but I'll call it good for now.

Quzah.

If you have covered pointers then you can see that a an array is really nothing more then a pointer and an offset.

Whenever I see something like "an array is a pointer", I recommend reading Q6.9, Q6.8, Q6.3, and Q6.2 as follow-up material.

say you want to access array[9]
with a pointer you would do this
*(array + 8).

No, array[9] and *(array + 9) are equivalent.