C++ Matrix Multiplication

[bpurificacion]

Hey can anybody help me find a way to input values from the keyboard into a 3 X 3 matrix. I'm having difficulty with even the simplist task.

here's what i have so far.

#include <iostream>
#include <fstream>

using namespace std;

const int SIZE = 3;

int row;
int col;
int PBUF[3][3];
int QBUF[3][3];
int RBUF[3][3];


int main()
{
int choice;

do
{
cout << endl
<< "Choose 1 to input two arrays from the keyboard.\n"
<< "Choose 2 to input two arrays from a file.\n"
<< "Choose 3 to display the input file data, buffer data, and output file data.\n"
<< "Choose 4 to write input file data, buffer data, and output file' on a file.\n"
<< "Choose 5 to exit the program";
cin >> choice;

switch (choice)
{
case 1:
{

for( col = 0; col < SIZE ; col ++ )
for( row = 0; row < SIZE; row ++ )
cin >> PBUF[col][row];
}
{
for( col = 0; col < SIZE ; col ++ )
for( row = 0; row < SIZE; row ++ )
cin >> QBUF[col][row];
}
cout << endl;
break;

case 2:

break;

case 3:

break;

case 4:

break;

case 5:
cout << "End of program.\n";
break;
default:
cout << "Not a valid choice.\n"
<< "Choose again.\n";
}
} while (choice !=5);

return 0;
}

[boxfish]

Hi,
I don't know if your compiler might be different, but on my compiler, the only problem is that SIZE is already defined by some built-in library or other. I renamed SIZE to some other name and your program worked perfectly. Hope this helps.

[bpurificacion]

i keep getting 2 errors its weird. im not sure if its my computer or my compiler. im using visual studio 2008 and i get these 2 errors

1. MSVCRTD.lib(crt exew.obj) : error LNK2019: unresolved external symbol _WinMain@16 referenced in function ___tmainCRTStar tup
2. fatal error LNK1120: 1 unresolved externals

Anybody have any suggestions?

[Studlyami]

Builds find in VS 2005, but it sounds like you didn't start an empty project. Create a new project, select win32 console app. Then click on application settings and select the check box for empty project. Create a .cpp file and paste your code into there and it should work fine.

[bpurificacion]

Thanks it actually does work now!

ok sorry for being such a newbie. But i also have to input two matrices from a file. do i need to call the file as in

char *inputfnameP = "inputPBUF.txt" ;
ifstream in_data;

in_data.open(in putfnameP);
if (in_data.fail() )
cout << "Unable to open 'inputPBUFF' for input." << endl;
}
{
char *inputfnameQ = "inputQBUF.txt" ;
ifstream in_data;

in_data.open(in putfnameQ);
if (in_data.fail() )
cout << "Unable to open 'inputQBUF' for input." << endl;
}

or am i doing this completely wrong. I also don't understand where the file must be located at. does it have to be in a specific folder or anything?

[weaknessforcats]

If you opne the file with a name like "input.txt" , the file has to be in the present working directory, which for Visual Studio.NET is the project folder (unless its .NET 2003 which has a bug here). Unless you have changed this folder in your project properties. Otherwise, you specify the complete path: "C:\\MyStuff\\T heDataFiles\\in put.txt".

[bpurificacion]

If you opne the file with a name like "input.txt" , the file has to be in the present working directory, which for Visual Studio.NET is the project folder (unless its .NET 2003 which has a bug here). Unless you have changed this folder in your project properties. Otherwise, you specify the complete path: "C:\\MyStuff\\T heDataFiles\\in put.txt".

I am using Visual Studio 2008.. I still don't understand how this all works.. Sorry! :(

[Laharl]

You've got to locate the folder where Visual Studio stores your project and make sure the file is in that folder. There's probably also a new file dialog you could use (just make an empty file, rather than one for a specific language, and save it as a .txt or whatever), if you can't find the folder.

[bpurificacion]

I was wondering how i would be able to multiply the values of the 2 matricies. The values were loaded into a buffer like PBUFF[3][3]. I was thinking about doing a for loop possibly, but i don't know how to multiply the first values of each array and then the second values.

for (row=0; row < 3; row ++)
for (col=0; col < 3; col ++)

[Laharl]

You'll need to write a function to do that, since C++ doesn't have a builtin function for it. This is a great tutorial on how (multidimension al) arrays work. Even if you think you understand them, as you read this, you will learn things.