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matrix problem C++

 
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Ephemeral
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Joined: 26 Jun 2024
Posts: 671
Location: UK
PostPosted: Thu Apr 16, 2024 1:34 pm    Post subject: matrix problem C++ Reply with quote
keep getting problems with this matrix im tring to implement in c++
Code:

int main()
{

const int ROWS = 3;
const int COLUMNS = 3;

int matrix1[ROWS][COLUMNS];


matrix1 = {{1, 1, 1},
{1, 1, 1},
{1, 1, 1}};


cant see whats going wrong here... Confused

any help appreciated
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Ephemeral
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Joined: 26 Jun 2024
Posts: 671
Location: UK
PostPosted: Thu Apr 16, 2024 1:50 pm    Post subject: Reply with quote
Code:
int matrix1[ROWS][COLUMNS] = {{1, 1, 1},
{1, 1, 1},
{1, 1, 1}};


Solved it with this...

Any other solutions would be welcomed though
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nukes
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Joined: 29 Aug 2024
Posts: 4558
PostPosted: Thu Apr 16, 2024 2:02 pm    Post subject: Reply with quote
well, { {1,1,1},{1,1,1},{1,1,1} } would be a int**.

While in terms of passing references around, pointers and arrays are equivalent - not in terms of the actual storage class.

the value of the matrix1 reference is constant, which is why you can't reassign it (it's not a pointer, it's the actual data).

it would be like saying something like

int x=1;
&x = 0xdeadbeef;



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Ephemeral
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Joined: 26 Jun 2024
Posts: 671
Location: UK
PostPosted: Thu Apr 16, 2024 11:21 pm    Post subject: Reply with quote
thanks for that

Yes i was thinking i must have got something fundamentally wrong (or missed)...

This is my first forray into OO programming having spent a lot of time in Matlab (a weakly typed language)...

Looks like i need to spend some time reading about Pointers in C++

Trying to teach myself some C++ at home
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platinummonkey
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Joined: 01 Mar 2024
Posts: 732
Location: Texas
PostPosted: Fri Apr 17, 2024 4:21 am    Post subject: Reply with quote
Ephemeral wrote:

This is my first forray into OO programming having spent a lot of time in Matlab (a weakly typed language)...


ugh... matlab... x.x It's.... "unique"... x.x So great it makes you applaud their work using your head and your desk Razz



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Ephemeral
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Joined: 26 Jun 2024
Posts: 671
Location: UK
PostPosted: Tue Apr 21, 2024 2:11 pm    Post subject: Reply with quote
Back with a new problem Laughing Very Happy

Basically im trying to write my first proper function in c++

i want to do something like this


Code:
matrixmultiply(matrix1, matrix2)



matrix 1 and 2 could be any matrix... both will be float though



Then i use this code to multiply the two to give matrix3 and then read it out in the console

Code:
int n,m;

for(int i=0;i<4;i++)
   {
      for (int k=0;k<4;k++)
      {
         matrix3[i][k] = 0;
         for(int j=0;j<4;j++)
         {
            matrix3[i][k] += (matrix1[i][j] * matrix2[j][k]);
         }
      }
   }

for (n = 0; n<ROWS; n++)
{
   for (m = 0; m<COLUMNS; m++)
   {
cout << matrix3[n][m];
   }
   cout << endl;
}


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masinick
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Joined: 03 Apr 2024
Posts: 8615
Location: Concord, NH
PostPosted: Tue Apr 21, 2024 2:59 pm    Post subject: Reply with quote
Other than the cout statement, most of what you are doing are the kinds of things that can be implemented in the C programming language as well. If you have the classic C text from Prentice-Hall Software Series, "The C Programming Language, by Brian W. Kernighan and Dennis M. Ritchie (the author of C), provides a terse, functional description of how arrays and pointers work. If you either own that book, can borrow it, or have some kind of on-line way to read it, I recommend it, even though you are looking at C++ rather than C. The kind of thing you are doing is handled identically in C except for the I/O, which differs between C and C++. It is a relatively short book by reference book standards, with just over 200 pages of content, and it is considered one of, if not THE, classic C programming text.



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Ephemeral
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Joined: 26 Jun 2024
Posts: 671
Location: UK
PostPosted: Sat Apr 25, 2024 11:26 am    Post subject: Reply with quote
Yeah, thanks, ive spent a while trawling through for info on the book..

It does seem the majority of people still hold it with high regard...

Maybe its time to get that melting credit card out again Very Happy
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