SIZE = 4

# Author:  James Tam
# Version: May 25, 2021
# Learning concepts: how to properly (and improperly) copy data from 
# one list to another.

#Copy data from list to another requires that the program manually copies
#each list element from one list to another.
def copy(destination,source):
    for r in range (0,SIZE,1):
        for c in range (0,SIZE,1):
            destination[r][c] = source[r][c]

# Creating reference to grid
def create():
    aGrid = [["*","*","*","*"],
             ["*","*","*","*"],
             ["*","*","*","*"],
             ["*","*","*","*"]]
    return(aGrid)


def display(aGrid):
    # Displaying the grid
    for r in range (0,SIZE,1):
        for c in range (0,SIZE,1):
            print(aGrid[r][c], end="")
        print()


def start():
    aGrid1 = create()
    print("Original list")
    display(aGrid1)
    
    #Not copying of lists aGrid1 & aGrid2 refer to the same 2D list
    print("\nINCORRECT: both aGrid1, aGrid2 refer to the same list")
    aGrid2 = aGrid1
    aGrid1[3][3] = "!" #Modifies same list! 
    print("First list")
    display(aGrid1)
    print("Second list")
    display(aGrid2)

    #Copying data from list to another
    print("\nCORRECT: aGrid1 and aGrid2 refer to two separate lists")
    aGrid2 = create() #Create new list otherwise aGrid2 would still refer to same list as aGrid1
    copy(aGrid1,aGrid2)
    aGrid1[0][0] = "?" 
    aGrid1[3][3] = "?" 
    print("First list")
    display(aGrid1)
    print("Second list")
    display(aGrid2)

start()