# Read a 4x4 matrix from user input

• 11-28-2005
JHaney
Read a 4x4 matrix from user input
I need to read in a user input matrix in the following format:

Please enter a 4x4 matrix one row at a time.

Row 1: 1 3 -1 0

Row 2: 2 4 1 0

Row 3: 3 2 -2 2

Row 4: 4 0 1 5

I need to use the function:
void getmatrix(double A[][4]);

I then have to call it from the function main().

I have other things to do but I think I can figure that stuff out if I can figure out how to read in the matrix.

Any help would be appreciated.
• 11-28-2005
Dae
Search google for "matrix c++" or just matrices, or any combo of the three. Theres tons of tutorials and code. Its pretty simple too.

As for void getmatrix(double A[][4]);, I'm not sure why its called getmatrix, instead of setmatrix, but you could just create a temp array (matrix) in main() and when you're done use that as the parameter for getmatrix().
• 11-29-2005
7stud
Quote:

I'm not sure why its called getmatrix
...beause the function gets the matrix from the user.

JHaney,

Pretend the function prototype is this instead:

void getmatrix(double A[4]);

and you have to read in this data:

Row 1: 1 3 -1 0

How would you do it? Write the code, and get it to work.

Once you get that working, you should be able to put that in a for loop and do it 4 times by letting the leftmost index value in the original function prototype vary with the loop index.
• 11-29-2005
Dae
Quote:

Originally Posted by 7stud
...beause the function gets the matrix from the user.

A right, I was looking at it as if it were in a class.

Edit: Ignore my first post. I was so out of it I assumed this function was part of a class and you were trying to set the matrix in that class by calling a function, but could only put it in one line at a time.
• 11-29-2005
jlf029
Code:

```void getmatrix(double A[][4]) {                int row=0;                 for(int i=0;i<4;i++)         {                 cout << "Row " << i+1 << ": ";                 for(int j=0;j<4;j++)                         cin >> A[i][j];         }                  }```
Is this something that you want to do? I had one sitting around, maybe it is useful for you to get the idea of how arrays are passed by reference
• 11-29-2005
7stud
Hey jlf029,

What do you think you're doing? Knock it off. :mad:
• 11-29-2005
JHaney
Thanks J. Yours is what I'm looking for. thanks
• 11-29-2005
JHaney
Alright I'm stuck again. I now have to find the minor of a 4x4 matrix.
• 11-29-2005
Dae
• 11-29-2005
jlf029
That link is good ^ except I had a good think about how I would find the minor but I can't seem to find a general solution. You would have to somehow use recursion. It's really hard to use loops as to find the minor you have to follow the rules of multiplication