8x8 Matrix and Loops

Using Arduino Programming Questions
2

You could try putting the loops into a function that draws a single square, then call that function for each of the corners in turn

void drawSquare(int top, int left,int width){
    int x;
    for(x=top; x<=(top+width); x++){
        matrix.drawPixel(left, x, LED_ON);
        ...
    }
    for(x=left+1; x<=(left+width); x++){
        matrix.drawPixel(x, top+width, LED_ON);
        ...
    }
    etc...
}