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    <p>This answer is total overkill, but this is my <code>struct</code> based approach which n.m. called "a whole 'nother story."</p> <p>If this is a new program (i.e. you get to define what the input / output to your function looks like) and you intend to do a lot of work with matrices, I would be inclined to use a struct to represent a matrix, and just pass around pointers to instances of that struct. </p> <p>The code below shows one possible approach. Note there are a couple "tricks" going on here. First of all, the data is all stored in a single contiguous block--this is likely to improve performance for a number of reasons. One potential downside to this technique is that resizing a matrix becomes expensive since you have to allocate an entirely new instance and copy data. But if you find that to be a problem, you can always change your implementation, assuming you always use matrix_get() and matrix_set() functions to access values in the matrix.</p> <p>Also, the matrix struct and the memory that data pointer points to is all allocated in a single malloc call. If you use this technique, just be aware that of data alignment issues. For example, if you change data to point to 64-bit integers or doubles, you'll need to add padding to make sure everything is 8-byte aligned. Alternatively, just <code>malloc</code> the data pointer as a separate array in the <code>new_matrix()</code> function, provided you remember to free it in <code>free_matrix()</code>.</p> <p>I've left as an exercise to the OP to write the multiply function. </p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; struct matrix { int rows; int cols; int * data; }; struct matrix * new_matrix( int rows, int cols ) { struct matrix * m = NULL; /* Allocate a block of memory large enough to hold the matrix 'header' struct * as well as all the row/column data */ m = malloc( sizeof(struct matrix) + (rows * cols * sizeof(int) ) ); if( m ) { m-&gt;rows = rows; m-&gt;cols = cols; /* Some ugly pointer math to get to the first byte of data */ m-&gt;data = (int*) ( (char *) m + sizeof(*m) ); } return m; } void free_matrix( struct matrix * m ) { free( m ); } int matrix_set( struct matrix * m, int row, int col, int val) { if( col &gt;= m-&gt;cols || row &gt;= m-&gt;rows ) return -1; m-&gt;data[ m-&gt;cols * row + col ] = val; return 0; } int matrix_get( struct matrix * m, int row, int col, int * val) { if( col &gt;= m-&gt;cols || row &gt;= m-&gt;rows ) return -1; else { *val = m-&gt;data[ m-&gt;cols * row + col ]; return 0; } } void print_matrix( struct matrix * m ) { int r,c; int val; for( r = 0; r &lt; m-&gt;rows; r++ ) { for( c = 0; c &lt; m-&gt;cols; c++ ) { matrix_get( m, r, c, &amp;val ); printf( "%5d%s", val, c + 1 &lt; m-&gt;cols ? "," : "" ); } printf("\n"); } } int main (int argc, char **argv) { int r,c; struct matrix * m = new_matrix( 5, 5 ); for( r = 0; r &lt; m-&gt;rows; r++ ) { for( c = 0; c &lt; m-&gt;cols; c++ ) { matrix_set( m, r, c, (r +1)* 10 + c + 1 ); } } print_matrix( m ); free_matrix( m ); return 0; } </code></pre>
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