How to read matrix recursively c++ - c++

Question

Can anyone help me with understanding recursion? I want to read a matrix recursively, and I don't really know how.
I made up a plan of transforming iterative agorithms to recursive ones in the following steps:
Repetitive structure-> if followed by recall of function somewhere in the body
Going from "top" to 0 and the going back to be alike the iterative way (i'm new to the concept, the idea may be dumb)
My function to read a matrix recursively (not working) is as follows:
void read_m(int n,int m)
{
if(n)
{
if(m)
{
read_m(n,m-1);
}
f>>v[n][m];
read_m(n-1,m);
}
}
I know what the mistake is, what I do not know is how should I solve this.
Thanks in advance.
P.S. n and m are width and height

Answer 1

Using recursion is probably not the greatest way to do this here but assuming you want it and you want the 'f' to execute for all the elements, it isn't going to work when n is 0 as it is inside the if(n) block.

Answer 2

first you should move f>>v[n][m];out if (n) block or it will not fill entire row with index 0.
second assuming that you keep data row by row you should read data before going to recursion, also to prevent double read you should only decrease rows when full column is read.
void read_m(int n,int m)
{
f>>v[width-1-n][height-1-m]; //suppose that width and height defined elsewhere
if(m)
{
read_m(n,m-1);
}
else if(n)
{
read_m(n-1,m);
}
}
if it is column by column you should change m and n in your code.

Answer 3

#include<fstream>
using namespace std;
ifstream f("recurs.in");
ofstream g("recurs.out");
int a[20][20],n,m;
void read(int i, int j)
{
if(j>1)
read(i,j-1);
else if(i>1)
read(i-1,j);
f>>a[i][j];
}
int main()
{
int i,j;
f>>n>>m;
read(n,m);
for(i=1;i<=n;i++)
{
for(j=1;j<=m;j++)
g<<a[i][j]<<' ';
g<<endl;
}
}
Working