Search code examples
pythonturtle-graphicspython-turtle

What does the code line if board [i][j]==0 do?

So I found this code online because I wanted to make my own so I like tried to understand what this person was doing by looking what all the different lines do, but i came across this line and I don't know what it does. I can't really find anything on this online, mostly because i don't know how to look it up or what it's called. It's a piece of code from the game connect 4, and this is the function for drawing the circles. I'm talking about the

if board[i][j]==0:

and

if board[i][j]==1:

code. It's in this little function:

def draw_pieces(): #draws the pieces
    global board #makes 'board' global
    row_gap = HEIGHT/ROWS #variable row_gap is now 771,4 / 6 = 128,6 (gap between circles)
    col_gap = WIDTH/COLS #variable col_gap is now 900 / 7 = 128,6 (gap between circles)
    Y = STARTY + row_gap / 2; # Y is now -385,7 + 128,6 / 2 = -321,4 
    for i in range(ROWS): #this next function happens 6 times (i think its first black their turn)
        X = STARTX + col_gap/2 #X is now -450 + 128,6 / 2 = -385,7
        for j in range(COLS): #this next function happens 7 times (then red their turn)
            if board[i][j] == 0: #if board i and j are equal to 0??
                draw_circle(X,Y,row_gap/3,'white') #draw a circle on X and Y, radius row_gap/3 and in color white
            elif board[i][j] == 1: #if board i and j are equal to 1??
                draw_circle(X,Y,row_gap/3,'black') #draw a circle on X and Y, raduis row_gap/3 and in color black
            else: #if board i and j are equal to anything else??
                draw_circle(X,Y,row_gap/3,'red') #draw a circle on X and Y, radius row_gao/3 and in color red
            X += col_gap #for every j, X is now added with col_gap (128,6)
        Y += row_gap #for every i, Y is now added with row_gap (128,6)

excuse all my comments on every line, I'm trying to understand the code. If someone can help me with this (or share a website or doc that explains it) that would be greatly appreciated!

Solution

  • If we look at the source and illustration of this game from pythonturtle.academy we can see more clearly what the code does:

    enter image description here

    The two dimensional board matrix stores one of three values, 0 for 'white' or unoccupied, 1 for 'black', the 1st player and 2 for 'red', the 2nd player. So the code in question is drawing circles on the board whose color is based on who occupies, (or doesn't occupy) the row and column, [i][j], in question:

    if board[i][j] == 0:
    draw_circle(X,Y,row_gap/3,'white')
elif board[i][j] == 1:
    draw_circle(X,Y,row_gap/3,'black')
else:
    draw_circle(X,Y,row_gap/3,'red')

    The else: clause is an implicit elif board[i][j] == 2: