Draw symmetric shape with randomized size and location

#include <iostream>
#include <string>
#include <cstdlib> // rand(), srand()
#include <ctime> // time()
using namespace std;

// This program draws three trees on a canvas. The location and size of the trees are chosen randomly.

int tree_sizes[] = { 3, 4, 5, 6, 7, 8 }; // Available tree sizes (number of rows of leaves)
const int canvas_width = 60; // Horizontal space available to draw trees
const int canvas_indent = 15; // Canvas begins in column number 16.
// The trunk is the same for all trees.

// This function draws a tree.
void draw_tree(int size, int placement, string leaf = "@", string trunk = "H", string space = " ", string margin_symbol = "`", int margin = 2)
{
    int midline = placement - 1; // Column index of the middle of the tree
    int num_rows = size; // Number of rows of leaves
    int side_margin = margin; // Space between the tree and the side of the box the tree is drawn in
    string leaf_symbol = leaf; // Symbol used for the tree leaves
    string trunk_symbol = trunk; // Symbol used for the tree trunk
    string space_symbol = space; // Symbol used outside the box the tree is drawn in
    string side_margin_symbol = margin_symbol; // Background symbol for area within the box that is not the leaves or the trunk

    // Draw the leaves.
    for (int row = 0; row < num_rows; ++row) // For each row of leaves,
    {
        for (int column = 0; column <= (midline + (num_rows - 1) + side_margin); ++column) // For each column in the box,
        {
            if ((column >= midline - row) && (column <= midline + row)) // If the column is part of the leaves,
            {
                cout << leaf_symbol; // Draw a leaf.
            }
            // Else if the column is between the tree and the box the tree is drawn in,
            else if (((column >= (midline - (num_rows - 1) - side_margin)) && (column < (midline - row))) ||
                ((column > (midline + row)) && (column <= (midline + (num_rows - 1) + side_margin))))
            {
                cout << margin_symbol; // Draw the background symbol.
            }
            else // Otherwise,
            {
                cout << space_symbol; // Draw a space.
            }
        }
        cout << endl; // Go to the next line.
    }

    // Draw the trunk.
    for (int row = 0; row < 2; ++row) // For the height of the trunk,
    {
        for (int column = 0; column <= (midline + (num_rows - 1) + (side_margin * 2)); ++column) // If the column is on the canvas,
        {
            if (column == midline) // If the column is the middle of the tree,
            {
                cout << trunk_symbol; // Draw the trunk.
            }
            // Else if the column is part of the background,
            else if (((column >= (midline - (num_rows - 1) - side_margin)) && (column < midline)) ||
                ((column > midline) && (column <= (midline + (num_rows - 1) + side_margin))))
            {
                cout << margin_symbol; // Draw the background.
            }
            else // Otherwise,
            {
                cout << space_symbol; // Draw a space.
            }
        }
        cout << endl; // Go to the next line.
    }
}

int main()
{
    int tree_size = 0; // Number of rows of leaves
    int num_trees = 3; // How many trees to draw
    int tree_location = 0; // Column number of tree horizontally
    int num_possible_locations = 0; // Number of columns that could have the midline of the tree

    srand(time(NULL)); // Prepare the random number generator.

    for (int i = 0; i < num_trees; ++i) // For each tree,
    {
        tree_size = (rand() % 6) + 3; // Pick a tree size between 3 and 8.
        // Determine the range of locations for the tree midline within the canvas.
        num_possible_locations = (canvas_width - (tree_size - 1) - 2) - (canvas_indent - (tree_size - 1) - 2);
        tree_location = (rand() % num_possible_locations) + (canvas_indent + 1); // Pick the tree midline.
        tree_size = (rand() % 6) + 3; // Pick a tree size between 3 and 8.
        draw_tree(tree_size, tree_location); // Draw tree.
    }

    return 0;
}