Having Trouble with matrix input (const variables)

[sparkythetiger]

I ran into a problem while trying to write a matrix program. Basically, what I'm trying to do is make a function INPUT that inputs a matrix from the user. I am having a lot of trouble with the const term at the beginning. Here is what I have so far. Is there any way you can help me?


#include <iostream>

using namespace std;

const int size = 10; // *THIS LINE HAS CAUSED MANY ERRORS

void INPUT( double[][ size ], int, int );
void OUTPUT( double[][ size ], int, int );

int main()
{
char stay = 'y';
int i, j;
int A[ i ][ j ]; // *SAME FOR THIS ONE

cout << &quot;This program manipulates matrices.&quot; << endl;
while ( stay == 'y' ) {

cout << &quot;How many rows?&quot;;
cin >> i;
cout << &quot;How many columns?&quot;;
cin >> j;
INPUT( A, i, j ); // *WHY DOES THE COMPILER SAY i AND j
OUTPUT( A, i, j ); // ARE SUPPOSED TO BE CONSTANTS???


cout << &quot;Enter the number of what you want to do:&quot; << endl << endl
<< &quot;1) Add a single variable to the matrix&quot;
<< &quot;2) Subtract a single variable from the matrix&quot;
<< &quot;3) Add another matrix to the matrix&quot;
<< &quot;4) Subtract another matrix from the matrix&quot;
<< &quot;5) Multiply by another matrix&quot; << endl << endl;

cin >> object;

switch ( object ) {

case 1:

break;

case 2:

break;

case 3:

break;

case 4:

break;

case 5:

break;

default:
cout << &quot;Incorrect number.. Enter 1, 2, 3, 4, or 5!&quot; << endl;
continue;

}

cout << endl << &quot;Do you wish to continue with a new matrix? (y or n)&quot; << endl;
cin >> stay;
cout << endl;
}

return 0;
}

void INPUT( double M[][ size ], int r, int c)
{
for( int i = 0; i < r; i++ ) {
for( int j = 0; j < c; j++ )
cout << &quot;Enter array element at row &quot; << i
<< &quot; and at column &quot; << j << &quot; &quot;;
cin >> M[ i ][ j ];
}
}

void OUTPUT( double M[][ size ], int r, int c )
{
for( int i = 0; i < r; i++ ) {
for( int j = 0; j < c; j++ )
cout << M[ i ][ j ] << &quot; &quot;;
cout << endl;
}
}

 

[BoulderBum]

There are two problem I see.

1. You are trying to use i and j before initializing them when you use them in the &quot;int A[ i ][ j ];&quot; delaration, but this doesn't matter because...

2. When initializing an array, the number of elements needs to be a constant integer. i and j are not constants, so &quot;int A[ i ][ j ]; &quot; blows up.

I can't remember if I've constanted casted at run-time to define array initialization (does anyone out there know if this is possible?), but try to do so first (search for const_cast on the internet), then tell me if you are unsuccessful, and I'll tell you how to initialize arrays using pointers and &quot;new&quot;.