Addition of 'n' matrices

[negru]

I have a matrix structure (for storing squared matrices)
which is defined as

typedef struct
{
    int **matrix;
    int format;
}MATRIX;

How to add 'n' number of matrices?

[gusano79]

Same as you'd add n numbers: Initialize a "sum" matrix to all zeros, then add matrices 1..n to the sum.

[negru]

@gusano79 Could you check the code (I have some segmentation faults, can't find what is wrong).
Also, could you show (in the code) how to add 'n' matrices?

#include<stdio.h>
#include<stdlib.h>
#define MAX 10
typedef struct
{
    int **matrix;
    int format;
}MATRIX;
void read_matrix(MATRIX *pm)
{
   do
   {
       printf("format=");
       scanf("%d",&pm->format);
   }
   while(pm->format < 1 || pm->format > MAX);
   pm->matrix=(int **)calloc(pm->format,sizeof(int *));
   int i,j,b=0;
   for(i=0;i<pm->format;i++)
   {
      pm->matrix[i]=(int *)calloc(pm->format,sizeof(int));
      for(j=0;j<pm->format;j++,b++)
        pm->matrix[i][j]=b;
   }
   for(i=0;i<pm->format;i++)
   for(j=0;j<pm->format;j++)
   {
       printf("mat[%d][%d]",i,j);
       scanf("%d",&pm->matrix[i][j]);
   }
}

void addition(MATRIX *array,int *n,MATRIX *res)
{
   array=(MATRIX *)malloc(*n * sizeof(MATRIX));
   do
   {
       printf("number of matrices:");
       scanf("%d",n);
   }
   while(*n < 1);
   int i;
   for(i=0;i<*n;i++)
   {
       /*adding matrices?*/
   }
}

void print(MATRIX *pm)
{
    int i,j;
    for(i=0;i<pm->format;i++){
        for(j=0;j<pm->format;j++){
                printf("%d\t",pm->matrix[i][j]);
        }
    printf("\n");
    }
}

void erase_1(MATRIX *pm)
{
    int i;
    for(i=0;i<pm->format;i++)
        free(pm->matrix[i]);
    free(pm->matrix);
}

int main()
{
    MATRIX *array;
    MATRIX *result;
    int i,n;
    for(i=0;i<n;i++)
    {
        printf("%d. matrix:\n",i+1);
        read_matrix(array+i);
    }
    addition(array,&n,res);
    print(res);
    for(i=0;i<n;i++)
        erase_1(array+i);
    free(array);
    free(res);
    return 0;    
}

[gusano79]

First things first...

How is this even compiling? You use the name res which isn't defined anywhere; I assume you mean result.

I have some segmentation faults, can't find what is wrong

What compiler are you using? Does it report any warnings? It should.

VS2015 gives me:

main.c(78): warning C4700: uninitialized local variable 'n' used
main.c(81): warning C4700: uninitialized local variable 'array' used
main.c(83): warning C4700: uninitialized local variable 'result' used

array and result are pointers, but you never actually point them at anything, so they're pointing who knows where and that's why the segfaults. Create some MATRIX objects and use those.

could you show (in the code) how to add 'n' matrices?

First thing I'd do is refactor a little bit - make these things separate in your code:

• Creating new MATRIX objects
• Deleting them
• Reading them in
• Adding them

This will make the problem easier to approach; your code is a bit of a mess right now.

For the addition portion, start by considering addition of simple integers. How would you do that? Here's a suggestion to start with:

int Add(int *values, int numValues)
{
    // ...
}

If you can do that, then all you have to do is change int to MATRIX and figure out how to add two matrices, not n.