Passing a two dimensional array to a function in C

Question

#include <iostream>
#include <math.h>
#include <stdio.h>
#define column 3
#define row 3
#define share 3

int matrix_multiplication(int left_matrix[][column], int right_matrix[][column], int result_matrix[][column], int rows, int cols, int shared);

int A[][3] = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
},
B[][3] = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
}, C[3][3]; //initialize "hard coded" three matrices

int main() {
    matrix_multiplication(A, B, C, row, column, share); //passes address of each matrix to function
    return 0;
}

int matrix_multiplication(int left_matrix[][column], int right_matrix[][column], int result_matrix[][column], int rows, int cols, int shared) {
    int i, j, k;

    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {//stays within first column and row through first iteration
            for (k = 0; k < 3; k++)//ensures inner dimensions match with variable k i.e. ixk * kxj =ixj or A*B=C
                result_matrix[i][j] += right_matrix[i][k] * left_matrix[k][j]; //C programming has ability to perform matrix multiplication
            //Adds result of each operation to C matrix i.e. +=
            printf("%d\t", result_matrix[i][j]); //matrix C is composed of rows(i) and columns(j)
        }//new tab after each column iteration
        printf("\n"); //new line for each row iteration
    }
    return 0;
}

This code is an good example of passing multidimensional arrays to a function using pointers and printing multidimensional arrays after mutliplication. There are multiple ways to indicate pointers to the compiler. I recommend seeing the "Correct way of passing a 2 dimensional array into a function." for example:

/*void display(int (*p)[numcols],int numRows,int numCols)//First method//
void dispaly(int *p,int numRows,int numCols) //Second Method//
void dispaly (int p[][numCols],int numRows,int numCols)  //Third Method*/

Answer 1

Remove the column variable, and add this above the matrix_multiplication function declaration:

#define column 3

(You may also want to rename column to COLUMNS.)

In C++ you can also do this:

static const int column = 3;

or, in C++11:

constexpr int column = 3;

The idea behind all this is that all but the very first size of a multidimensional array must be known at compile time.

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To fix the expected primary-expression before ']' token" error, change your inner assignment to something like this:

result_matrix[i][j] += right_matrix[i][k] * left_matrix[k][j];

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Also you should initialize result_matrix with 0s first.

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Also remove the * from int *result_matrix[][column].

Most modern compilers display warnings if you pass an int instead of an int*. Please enable all warnings in your compiler, recompile, fix them, and update your question stating that the example code compiles cleanly, without warnings.

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To print an element of the matrix, you have to specify which element you want to print:

printf("%d\t", result_matrix[i][j]);

I can't believe that your compiler didn't display a warning when you omitted the [i][j]. Warnings are for your benefit: they indicate possible bugs in your code.