Comparison of two strings in Lua
https://stackoverflow.com//questions/20014311
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21-12-2019 - |
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I am trying to compare two strings where the first string is a single element of an array and the second array is just a regular string. For some reason, the comparison is not coming through as true. Hopefully, someone can point me in the right direction!
empty = " "
pawn = " Pawn "
rook = " Rook "
knight = " Knight "
bishop = " Bishop "
queen = " Queen "
king = " King "
emptyspot = {}
for i = 1, 8 do
emptyspot[i] = {}
for j = 1, 8 do
emptyspot[i][j] = " / "
end
end
function chessBoard()
io.write("\n\nWelcome to LuaChess!\n\n")
io.write(" 1 2 3 4 5 6 7 8 \n")
io.write(" *************************************************************************\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" A *".. emptyspot[1][1] ..
"*"..emptyspot[1][2].."*"..emptyspot[1][3].."*"..emptyspot[1][4]..
"*"..emptyspot[1][5].."*"..emptyspot[1][6].."*"..emptyspot[1][7].."*"..emptyspot[1][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" B *".. emptyspot[2][1] ..
"*"..emptyspot[2][2].."*"..emptyspot[2][3].."*"..emptyspot[2][4]..
"*"..emptyspot[2][5].."*"..emptyspot[2][6].."*"..emptyspot[2][7].."*"..emptyspot[2][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" C *".. emptyspot[3][1] ..
"*"..emptyspot[3][2].."*"..emptyspot[3][3].."*"..emptyspot[3][4]..
"*"..emptyspot[3][5].."*"..emptyspot[3][6].."*"..emptyspot[3][7].."*"..emptyspot[3][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n") io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" D *".. emptyspot[4][1] ..
"*"..emptyspot[4][2].."*"..emptyspot[4][3].."*"..emptyspot[4][4]..
"*"..emptyspot[4][5].."*"..emptyspot[4][6].."*"..emptyspot[4][7].."*"..emptyspot[4][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n") io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" E *".. emptyspot[5][1] ..
"*"..emptyspot[5][2].."*"..emptyspot[5][3].."*"..emptyspot[5][4]..
"*"..emptyspot[5][5].."*"..emptyspot[5][6].."*"..emptyspot[5][7].."*"..emptyspot[5][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n") io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" F *".. emptyspot[6][1] ..
"*"..emptyspot[6][2].."*"..emptyspot[6][3].."*"..emptyspot[6][4]..
"*"..emptyspot[6][5].."*"..emptyspot[6][6].."*"..emptyspot[6][7].."*"..emptyspot[6][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n") io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" G *".. emptyspot[7][1] ..
"*"..emptyspot[7][2].."*"..emptyspot[7][3].."*"..emptyspot[7][4]..
"*"..emptyspot[7][5].."*"..emptyspot[7][6].."*"..emptyspot[7][7].."*"..emptyspot[7][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n") io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" H *".. emptyspot[8][1] ..
"*"..emptyspot[8][2].."*"..emptyspot[8][3].."*"..emptyspot[8][4]..
"*"..emptyspot[8][5].."*"..emptyspot[8][6].."*"..emptyspot[8][7].."*"..emptyspot[8][8].."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *".. empty ..
"*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*"..empty.."*\n")
io.write(" *************************************************************************\n\n")
io.write(" Choose a piece to move and the location\n for it to be moved to separated by a space:\n")
end
function initBoard()
emptyspot[1][1] = rook
emptyspot[1][2] = knight
emptyspot[1][3] = bishop
emptyspot[1][4] = queen
emptyspot[1][5] = king
emptyspot[1][6] = bishop
emptyspot[1][7] = knight
emptyspot[1][8] = rook
emptyspot[8][1] = rook
emptyspot[8][2] = knight
emptyspot[8][3] = bishop
emptyspot[8][4] = queen
emptyspot[8][5] = king
emptyspot[8][6] = bishop
emptyspot[8][7] = knight
emptyspot[8][8] = rook
for i = 1, 8 do
emptyspot[2][i] = pawn
end
for i = 1, 8 do
emptyspot[7][i] = pawn
end
end
function swapPieces(piece1, piece2)
temp = piece1
piece1 = piece2
piece2 = temp
end
function movePawnPlayerOne(spot1, spot2)
spot1 = spot1 + 1
emptyspot[spot1][spot2] = pawn
print(emptyspot[spot1][spot2])
end
initBoard()
while true do
chessBoard()
--Take first input for movement
input = io.read("*line")
loc1 = string.sub(input,1,1)
loc2 = string.sub(input,2,2)
if((loc1 == "A") or (loc1 == "a")) then
loc1 = 1
end
if ((loc1 == "B") or (loc1 == "b")) then
loc1 = 2
end
if ((loc1 == "C") or (loc1 == "c")) then
ioc1 = 3
end
if ((loc1 == "D") or (loc1 == "d")) then
loc1 = 4
end
if ((loc1 == "E") or (loc1 == "e")) then
loc1 = 5
end
if ((loc1 == "F") or (loc1 == "f")) then
loc1 = 6
end
if ((loc1 == "G") or (loc1 == "g")) then
loc1 = 7
end
if ((loc1 == "H") or (loc1 == "h")) then
loc1 = 8
end
if (emptyspot[loc1][loc2] == pawn) then
movePawnPlayerOne(loc1, loc2)
end
print(emptyspot[3][1])
if string.find(input, "restart") then
initBoard()
end
if string.find (input, "exit") then
os.exit()
end
end
The piece of code in question is towards the bottom. Both emptyspot[][] and pawn are both strings.
Solution
input = io.read("*line")
loc1 = string.sub(input, 1, 1)
loc2 = string.sub(input, 2, 2)
You're reading the input in as strings but your emptyspot table uses numeric indices as keys. Try fixing it with:
loc2 = tonumber(string.sub(input, 2, 2))
OTHER TIPS
The answer from greatwolf is certainly the source of your immediate problem.
It is not that Lua can't compare the strings, but that you had actually looked up a non-existent element of the 2D array you indexed, and were always comparing nil to pawn as a result.
That said, I have a few comments about the rest of the code, and the problems you are going to encounter soon.
First, if you find yourself copying and pasting code to build up a large regular structure, look for opportunities to use loops and functions to abstract out the common elements. The monster function chessBoard is a good example. Fundamentally, what it does is print out the board, which is an array of 64 squares, where each square is printed with a certain amount of ASCII-art. As you have it written, the code that indexes each square's current piece is deeply entangled with the code that is drawing the rest of the square. When you discover that you would rather use a different notation for the pieces (for instance, to distinguish White from Black which you don't do now), you will have a mess on your hands to edit that monolithic collection of io.write built up with carefully constructed strings.
Second, consider separating the model even further from the view. The model in this case is of a chessboard, which is an array of squares that may be empty or contain one of several kinds of piece of two colors. The view is how you draw the board to present it to the user. Your code here blends model and view because the pieces themselves are represented in the model by the actual string used to present them to the user in the view. Recognizing that this abstraction exists is important as you move forward to implementing algorithms more complex than merely displaying the board and moving pieces.
Third, long chains of if statements that repeat the same test with different constants are almost always easy to turn in to much more compact (and more efficient) expressions.
You write if ((loc1 == "C") or (loc1 == "c")) then loc1=3 end for each of A to H. This can be simplified two ways. First, fold the input case so you are testing for a single case of character, then use string.find to convert from letter to integer at once. So the whole block of 8 if-then statements could be written as
loc1 = ("abcdefgh"):find(loc1:lower())
which will either make loc1 be an integer from 1 to 8, or nil if that character is not in the range A to H.
Fourth, io.write can take multiple arguments, which will be output consecutively without any delimiters (unlike print which inserts tabs between arguments and a newline at the end). So those long expressions in chessBoard() can have all of the string concatenation replaced with simple commas. This is not only faster, but it prevents the creation of a great deal of garbage for the garbage collector to eventually handle which comes from all of the temporary strings needed to complete the expression.
