Question

I am studying pointers in C/C++ and as my little project to learn this problematic I am trying to develop a simple application doing operations with matrixies. I want to ask if this way I am using pointers and dynamic allocation in is correct or I am making it wrong. Thanks 🙂

#include <stdlib.h>
#include <stdio.h>

int numberRows;
int numberCollumns;
void getSize()
{
   printf("Write down size of matrix in format Rows Collumns: ");
   scanf("%i %i", &numberRows, &numberCollumns);
}

void getMatrix(int *m[])
{
   int x = 0;
   int y = 0;
   while(x<numberRows)
   {
      while(y<numberCollumns)
      {
      scanf("%i", &m[x][y]);
      y++;        
      }
   x++;
   y = 0;
   }
}

void writeMatrix(int *m[])
{
   int x = 0;
   int y = 0;
   while(x<numberRows)
   {
      while(y<numberCollumns)
      {
      printf("%i ", m[x][y]);
      y++;        
      }
   printf("\n");
   x++;
   y = 0;
   }
}

int main()
{
   getSize();
   int **matrix;
   matrix = (int**)malloc(numberRows*sizeof(int*));
   int x = 0;
   while(x < numberCollumns)
   {
      matrix[x] = (int*)malloc(numberCollumns*sizeof(int));
      x++;
   }
   getMatrix(matrix);
   printf("\n\nMatrix: \n");
   writeMatrix(matrix);


   return 0;
}

Answer 1

I found a problem:

while(x < numberCollumns)
{
   matrix[x] = (int*)malloc(numberCollumns*sizeof(int));
   x++;
}

Your loop condition is wrong. What if the number of rows and columns do not match up?
Also, I do not seeing any corresponding calls to free.

As for code style, your while loops would look better as for loops:

for(int x = 0; x < numberRows; ++x)
{
    matrix[x] = (int*)malloc(numberCollumns*sizeof(int));
}

Side Note

The code is pure C (well except for the casting of the return from malloc). C++ code would look a lot different.