How to extract a 2x2 submatrix from a bigger matrix

Question

I am a very basic user and do not know much about commands used in C, so please bear with me...I cant use very complicated codes. I have some knowledge in the stdio.h and ct

Answer 1

Let's take this in stages. First a couple of minor fixes to your code:

for(i=0;i

Now we define what we want:

int startrow = 2; /* The starting index. Remember we index 0,1,2,3 */
int startcol = 2;
int resultrows = 2; /* How many rows we want in our answer */
int resultcols = 2;
float result[resultrows][resultcols];

Now we ignore what we don't want:

for(i=0;i= startrow && i < startrow + resultrows &&
       j >= startcol && j < startcol + resultcols){
      matrix[i][j] = dummy;
    }
  }
}

Notice that now only the values we want are copied into matrix, the rest of matrix is uninitialized gibberish. Now write it into result instead:

for(i=0;i= startrow && i < startrow + resultrows &&
       j >= startcol && j < startcol + resultcols){
      result[i-startrow][j-startcol] = dummy;
    }
  }
}

EDIT:
If you want to copy a submatrix from a larger matrix already in memory, the inner loop should be

for(j=0;j= startrow && i < startrow + resultrows &&
     j >= startcol && j < startcol + resultcols){
      result[i-startrow][j-startcol] = matrix[i][j];
  }
}