2d array relative to direction on grid - c++

I'm working on a program that hides a number in a grid (2d array, 10 columns and 10 rows labeled with array filled with a character such as a . or -) and prints the grid to screen.
a num for row and column are random generated and saved to array as an 'X', only shown when found
The user enters the row and column....then displays that user's guess on the grid to the screen as a character. after that, choose which direction to move...and give hints on where the randomized location for that item is hidden in the array within ten tries total or less(user cannot go to previous guess played during the program).
for example:
while (guess <9 || found == false){
cout << "Enter your next move....n, e, s, w, ne, nw, se, sw";
cin >> d;
if (d == 'E' || d == 'e')
{
col++;
guess++;
array[col][row] = guess;
cout << "moved east";
}
else if (d == 'W' || d == 'w')
{
col--;
guess++;
array[col][row] = guess;
cout << "west...";
}
....etc
else {
guess++;
cout << "not valid move. turn is incremented";
}
then after the entire while loop on all those, i display the array again but I can't get the moves to show up other than the first step(need it to do 1, 2, 3...10 or until found=true to display 'X') and am not sure how to give the hint on where the item is hidden based on guess direction. if the item is north above where the user guessed their first starting place(column and row), it should display hint based on that location. How could I implement that?

Must be: while(guess < 9&&!found), either condition not met shall leave to exiting, so you only stay in the loop if both are met... Side note: It is better code style not to compare booleans, just use if(condition) or if(!condition) as in the fixed loop condition.
Be aware that you should check your board's borders:if(col > 0)
{
--col;
++guess;Analogously for the other directions...
You need to check, if the field intended to visit already has been visited. Assuming the fields unvisited carry value 0, you can add the following condition to the border check:if(col > 0 && array[col - 1][row] != 0)Again, other directions analogously.
For the hints, calculate the distances of the coordinates between target and current position; if negative, add 'n' or 'w' to your hint for vertical or horizontal direction respectively, if positive, 's' or 'e', otherwise, no hint for the respective direction (easiest variant, prefers diagonal directions first).
Side note array[col][row]: Typically, you name the indices of the array the other way round: array[row][col]; if iterating, you use outer loop for rows, inner loop for cols (to profit from data locality):
for(r = 0; r < rows; ++r)
for(c = 0; c < cols; ++c)
std::cout << getCharFor(array[r][c]);
North and south, with code above, still are associated with vertical, east and west with horizontal direction...
Edit in response to your comment:
You do not need to check the border you are moving away from...if(d == "e")
{
if(/*col > 0 &&*/ col <= 10)
//^^^^^^^^^ obsolete...
}
If your array has a size of NxN, then the maximum index you can access is N - 1, so you only can go east if you are currently maximally at position N - 2 (if(col < N-1))
If you go diagonally, you have to check both horizontal and vertical direction:if(d == "sw")
{
if(row < N - 1 && col > 0)
}
If you have determined that you do not exit the board with the designated move, then you can access the field in the designated direction:if(d == "sw")
{
if(array[row + 1][col - 1] != 0)
// visited already; assuming you have initialized the array with 0...
}
Side note: For the hints, there is yet an unconsidered problem left: What, if the user does not follow them, and due to this, the program gives a hint to a field that already has been visited???

Related

Creating the Backtracking Algorithm for n-queen Problem [closed]

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I have tried to come up with a solution to the n-queen problem, through backtracking. I have created a board, and I think I have created functions which checks whether a piece can be placed at position column2 or not, in comparison to a piece at position column1. And I guess I somehow want to loop through the columns, to check if the current piece is in a forbidden position to any of the power pieces already placed at the first row through the current minus one. I haven't done this yet, but I'm just confused at the moment, so I can't really see how I should do it.
Let me share the code I have written so far
// Method for creating chessboard
vector<vector<vector<int>>> create_chessboard(int size_of_board)
{
vector<int> v1;
vector<vector<int>> v2;
vector<vector<vector<int>>> v3;
for (int i = 0; i < size_of_board; i++)
{
for (int j = 0; j < size_of_board; j++)
{
v1.clear();
v1.push_back(i);
v1.push_back(j);
v2.push_back(v1);
}
v3.push_back(v2);
v2.clear();
}
return v3;
}
// Method for visualizing chessboard
void visualize_board(vector<vector<vector<int>>> chess, int dimension_of_board)
{
int i = 1;
for (vector<vector<int>> rows : chess)
{
for (int j = 0; j < dimension_of_board; j++)
{
cout << "(" << rows[j][0] << "," << rows[j][1] << ")" << " ";
}
cout << endl;
}
}
// Method for checking if two coordinates are on the same diagonal
bool check_diagonal(vector<int> coordinate1, vector<int> coordinate2)
{
if(abs(coordinate1[1] - coordinate2[1]) == abs(coordinate1[0] - coordinate2[0]))
{
return true;
}
return false;
}
bool check_column(vector<int> coordinate1, vector<int> coordinate2)
{
if(coordinate1[1] == coordinate2[1])
{
return true;
}
return false;
}
bool check_row(vector<int> coordinate1, vector<int> coordinate2)
{
if (coordinate1[0] == coordinate2[0])
{
return true;
}
return false;
}
bool check_allowed_positions(vector<int> coordinate1, vector<int> coordinate2, int column)
{
if (check_diagonal(coordinate1, coordinate2))
{
return false;
}
if (check_column(coordinate1, coordinate2))
{
return false;
}
if (check_row(coordinate1, coordinate2))
{
return false;
}
return true;
}
vector<vector<int>> solve_nqueen(vector<vector<vector<int>>> board, int dimension_of_board, int row)
{
vector<int> first_element = board[0][0];
vector<vector<int>> solution_space;
if (dimension_of_board == row)
{
cout << "we found a solution!";
}
/*
if (dimension_of_board == row)
{
}
for (int j = 0; j < dimension_of_board; j++)
{
if (check_allowed_positions(board, row, j))
{
do something here
solve_nqueen(board, dimension_of_board, row+1);
}
else
{
do something here;
}
}
return;
*/
return solution_space;
}
I would be really happy if someone could just lay up a few steps I have to take in order to build the solve_nqueen function, and maybe some remarks on how I could do that. If I should complement with some further information, just let me know! I'm happy to elaborate.
I hope this isn't a stupid question, but I have been trying to search the internet for a solution. But I didn't manage to use what I found.
Best wishes,
Joel
There is not always a solution, like e.g. not for 2 queens on 2x2 board, or for 3 queens on a 3x3 board.
This is a well-known problem (which can also be found in the internet). According to this, there is not a simple rule or structure, how you can find a solution. In fact, you could reduce the problem by symmetries, but that is not that simple, too.
Well according to this, you have to loop through all (n out of n x n) solutions, and do all tests for every queen. (In fact, reduce it to half again, by only checking a certain pair of queens, once only - but again that is not much, and such reduction takes some time, too).
Note: Your check routines are correct.
For 8 queens on a 8x8 board, write 8 nested loops from i(x)=0 to 63
(row is i(x)%8 and column is i(x)/8). You also need to check then, if a queen does not sit on queen, but your check routines will already find that. Within second nested loop, you can already check if the first two queens are okay, or otherwise, you do not have to go any deeper, but can already increment the value of first nested loop (move the second queen on a new position).
Also it would be nice, I propose not to write the search for a n-problem, but for a n=8 problem or n=7 problem. (That is easier for the beginning.).
Speed-Ups:
While going deeper into the nested loops, you might hold a quick
record (array) of positions which already did not work for upper
loops (still 64 records to check, but could be written to be faster than doing your check routines again).
Or even better, do the inner loops only through a list from remaining candidates, much less than (n x n) positions.
There should be some more options for speed-ups, which you might find.
Final proposal: do not only wait for the full result to come, but also track, when e.g. you find a valid position of 5 queens, then of 6 queens and so on - which will be more fun then (instead of waiting ages with nothing happening).
A further idea is not to loop, e.g. from 0 to 63 for each queen, but "randomly". Which also might lead to more surprising. For this, mix an array 0 .. 63 to a random order. Then, still do the loop from 0 to 63 but this is just the index to the random vector. Al right? Anyway, it would even be more interesting to create 8 random vectors, for each queen one random vector. If you run this program then, anything could happen ... the first few trials could (theoretically) already deliver a successful result.
If you would like to become super efficient, please note that the queen state on the 8x8 board can be stored in one 64-bit-integer variable (64 times '0' or '1' where '1' means here is queen. Keyword: bitboards). But I didn't mention this in the beginning, because the approach which you started is quite different.
And from that on, you could create 64 bit masks for each queen position, to each position to which a queen can go. Then you only need to do 1 "bitwise AND" operation of two (properly defined) 64-bit variables, like a & b, which replaces your (diagonal-, column-, row-) check routines by only one operation and thus is much faster.
Avoid too many function calls, or use inline.
... an endless list of possible dramatic speed-ups: compiler options, parallelization, better algorithms, avoid cache misses (work on a possibly low amount of memory or access memory in a regular way), ... as usual ...
My best answer, e.g. for 8-queen problem:
queen is between 0 .. 7
queen is between 8 .. 15
queen is between 16 .. 23
queen is between 24 .. 31
queen is between 32 .. 39
queen is between 40 .. 47
queen is between 48 .. 55
queen is between 56 .. 63
because all 8 queens have to be on different rows!
These are the limits of the nested loops then, which gives "only"
8 * 8 * 8 * 8 * 8 * 8 * 8 * 8 = 16777216
possibilities to be checked. This can be quick on modern machines.
Then probably you don't need anything more sophisticated (to which my first answer refers - for the 8x8 queens problem.) Anyway, you could still also keep a record of which column is still free, while diving into the nested loops, which yields a further dramatic cut down of checks.
I wrote some C code (similar to C++) to verify my answer. In fact, it is very fast, much less than a second (real 0m0,004s; user 0m0,003s; sys 0m0,001s). The code finds the correct number of 92 solutions for the 8x8 queens problem.
#include <stdio.h>
int f(int a, int b)
{
int r1, c1, r2, c2, d1, d2;
int flag = 1;
r1 = a / 8;
r2 = b / 8;
c1 = a % 8;
c2 = b % 8;
d1 = r1 - r2;
d2 = c1 - c2;
if( d1 == d2 || d1 == -d2 || c1 == c2 ) flag=0;
return flag;
}
int main()
{
int p0,p1, p2, p3, p4, p5, p6, p7;
int solutions=0;
for(p0=0; p0<8; p0++)
{
for(p1=8; p1<16; p1++)
{
if( f(p0,p1) )
for(p2=16; p2<24; p2++)
{
if( f(p0,p2) && f(p1,p2) )
for(p3=24; p3<32; p3++)
{
if( f(p0,p3) && f(p1,p3) && f(p2,p3) )
for(p4=32; p4<40; p4++)
{
if( f(p0,p4) && f(p1,p4) && f(p2,p4) && f(p3,p4))
for(p5=40; p5<48; p5++)
{
if( f(p0,p5) && f(p1,p5) && f(p2,p5) && f(p3,p5) && f(p4,p5) )
for(p6=48; p6<56; p6++)
{
if( f(p0,p6) && f(p1,p6) && f(p2,p6) && f(p3,p6) && f(p4,p6) && f(p5,p6))
for(p7=56; p7<64; p7++)
{
if( f(p0,p7) && f(p1,p7) && f(p2,p7) && f(p3,p7) && f(p4,p7) && f(p5,p7) && f(p6,p7))
{
solutions++;
// 0 .. 63 integer print
printf("%2i %2i %2i %2i %2i %2i %2i %2i\n",
p0,p1,p2,p3,p4,p5,p6,p7);
// a1 .. h8 chess notation print
//printf("%c%d %c%d %c%d %c%d %c%d %c%d %c%d %c%d\n",
//p0%8+'a', p0/8+1, p1%8+'a', p1/8+1, p2%8+'a', p2/8+1, p3%8+'a', p3/8+1,
//p4%8+'a', p4/8+1, p5%8+'a', p5/8+1, p6%8+'a', p6/8+1, p7%8+'a', p7/8+1);
}
}
}
}
}
}
}
}
}
printf("%i solutions have been found\n",solutions);
return 1;
}
Notes: Subroutine f checks if two queen positions are "ok" with each other (1 means true, 0 means false, in C). An inner loop is only entered, if all already selected positions (in outer loops) are "ok" with each other.

if-statement executing when it shouldn't (kind of)

int trees = 3;
int tree_x, tree_y;
for(int r = 0; r < m_townsize; r++)
{
for(int c = 0; c < m_townsize; c++)
{
if(r == 0 || c == 0 || r == (m_townsize - 1) || c == (m_townsize - 1))
m_town[r][c] = 'W';
while(trees > 0)
{
tree_x = random() % m_townsize;
tree_y = random() % m_townsize;
cout << tree_y << "," << tree_x << endl;
if(m_town[tree_y][tree_x] == ' ')
{
m_town[tree_y][tree_x] = 'T';
trees -= 1;
}
}
}
}
According the code I have written, if there is a space character at the coordinate of the tree, it should place a tree and lower the tree count by 1.
If there is not a space there, it should skip placing a tree, thus not decrementing. This should cause it to pick another set of coordinates and run through again.
However, if you look at this particular output it is running to the if-statement skipping the first option to replace it with a T--since it is a W--but still decrementing by 1. I don't get it. It should skip the statement all together, not skip just the first line. Netbeans tells me my brackets are right, so it shouldn't be an issue with the assignment belonging to the if and the decrement belonging to the while.
If I make a do-while loop it places a whole bunch. I don't know what's happening.
This output placed 2 trees.
You are walking over each coordinate.
If it is on the edge you put a 'W'. Then you randomly place a tree 'T'.
Then you proceed to the next coordinate.
This means you can place some trees in squares before you overwrite with a 'W'.
Finish all the walls before placing trees. Consider a more efficient way to place walls to, like doing each edge instead of loopimg over the middle abd doing nothing.

If-else statement in c++

i have a problem with the next question, i need to solve it by using if/else, i wrote the code but i don't know if it's the solve of the question or not:
Write a program in which the user enters the coordinates of the black pawns (a, b) on the chessboard.
The program must determine whether the pawn may move to get to one field (c, d):
1. In the ordinary move;
2. When it "hit" piece or pawn opponent.
Note: Black pawn move on the board from the bottom up.
char CoordinY;
int CoordinX;
if (CoordinY > 'b' && CoordinX <= 1 && CoordinX>8)
{
cout << "Error . . . \n";
}
else
{
if (CoordinX >= 2 && CoordinX <= 8 && CoordinY == 'a' || CoordinY == 'b'*)
{
// arbitrary move:
cout << "will not get to the field (c, d) in the ordinary move.\n";
// when it "hits" enemy's figure or pawn
cout << "will not get to the field (c, d) when ше hit a figure or pawn opponent.\n";
}
else if (CoordinX>1 && CoordinX < 8 && CoordinY == 'b')
{
// arbitrary move
cout << "will not get to the field (c, d) in the ordinary move.\n";
// when it "hits" enemy's figure or pawn
cout << "will not get to the field (c, d) when it hit a figure or pawn opponent.\n";
}
In the answer I assume the following classic chess board and the fact that I am moving white pawn:
It is important because in your problem definition, blacks are moving bottom up, which is incorrect.
In my example, I will use the following variables:
char a, c; int b, d; // E2 - E4 is: a = 'e', b = 2, c = 'e', d = 4.
Arbitrary move
Where can a pawn go with an arbitrary move in chess?
One step ahead
Two steps ahead if it is standing at row 2
So, in general, a pawn at (a; b) can move to (c; d), if they stand in the same row (a == c) AND if it is one step ahead or two steps ahead for b equal to 2.
So, let's implement it:
if (a == c && (d - b == 1 || (d - b == 2 && b == 2)))
cout << "Abitrary move: YES";
} else {
cout << "Arbitrary move: NO";
}
Attack
A pawn can move with an attack if only an enemy is standing in the next row, one cell to the left or to the right:
if ((c == a + 1 || c == a - 1) && (d - b == 1))
cout << "Attack: YES";
} else {
cout << "Attack: NO";
}
Note that this solution is not working for the case which is called en passant (is it more well-known as "битое поле" or "взятие на проходе" in Russian).
This is a solution in pseudocode:
if (d == b - 1) // destination is one square up
if (c == a) // pawn is on a square in the same column as destination
return true; // yes, pawn can move forwards to destination
if (c == a - 1 || c == a + 1) // destination is one square to left or right
return true; // yes, pawn can take a white pawn to move to destination
end if
return false
First we do the check which is true for both cases... is the destination only one step in front (note that in chess pawns can also move two squares on their first turn, but you didn't request that solution so I haven't added it)?
Next we check if the move is either straight ahead, or diagonal.
You might want to check that a,b c,d are all valid chess coordinates to start with, which would prevent illegal moves being marked as ok.
Edit: also I'm assuming that the bottom of the board has a larger 'y' coordinate than the top. If the coordinates are reversed you would check for b + 1 in the first conditional.

Determining if a number is either a multiple of ten or within a particular set of ranges

I have a few loops that I need in my program. I can write out the pseudo code, but I'm not entirely sure how to write them logically.
I need -
if (num is a multiple of 10) { do this }
if (num is within 11-20, 31-40, 51-60, 71-80, 91-100) { do this }
else { do this } //this part is for 1-10, 21-30, 41-50, 61-70, 81-90
This is for a snakes and ladders board game, if it makes any more sense for my question.
I imagine the first if statement I'll need to use modulus. Would if (num == 100%10) be correct?
The second one I have no idea. I can write it out like if (num > 10 && num is < 21 || etc.), but there has to be something smarter than that.
For the first one, to check if a number is a multiple of use:
if (num % 10 == 0) // It's divisible by 10
For the second one:
if(((num - 1) / 10) % 2 == 1 && num <= 100)
But that's rather dense, and you might be better off just listing the options explicitly.
Now that you've given a better idea of what you are doing, I'd write the second one as:
int getRow(int num) {
return (num - 1) / 10;
}
if (getRow(num) % 2 == 0) {
}
It's the same logic, but by using the function we get a clearer idea of what it means.
if (num is a multiple of 10) { do this }
if (num % 10 == 0) {
// Do something
}
if (num is within 11-20, 31-40, 51-60, 71-80, 91-100) { do this }
The trick here is to look for some sort of commonality among the ranges. Of course, you can always use the "brute force" method:
if ((num > 10 && num <= 20) ||
(num > 30 && num <= 40) ||
(num > 50 && num <= 60) ||
(num > 70 && num <= 80) ||
(num > 90 && num <= 100)) {
// Do something
}
But you might notice that, if you subtract 1 from num, you'll have the ranges:
10-19, 30-39, 50-59, 70-79, 90-99
In other words, all two-digit numbers whose first digit is odd. Next, you need to come up with a formula that expresses this. You can get the first digit by dividing by 10, and you can test that it's odd by checking for a remainder of 1 when you divide by 2. Putting that all together:
if ((num > 0) && (num <= 100) && (((num - 1) / 10) % 2 == 1)) {
// Do something
}
Given the trade-off between longer but maintainable code and shorter "clever" code, I'd pick longer and clearer every time. At the very least, if you try to be clever, please, please include a comment that explains exactly what you're trying to accomplish.
It helps to assume the next developer to work on the code is armed and knows where you live. :-)
If you are using GCC or any compiler that supports case ranges you can do this, but your code will not be portable.
switch(num)
{
case 11 ... 20:
case 31 ... 40:
case 51 ... 60:
case 71 ... 80:
case 91 ... 100:
// Do something
break;
default:
// Do something else
break;
}
This is for future visitors more so than a beginner. For a more general, algorithm-like solution, you can take a list of starting and ending values and check if a passed value is within one of them:
template<typename It, typename Elem>
bool in_any_interval(It first, It last, const Elem &val) {
return std::any_of(first, last, [&val](const auto &p) {
return p.first <= val && val <= p.second;
});
}
For simplicity, I used a polymorphic lambda (C++14) instead of an explicit pair argument. This should also probably stick to using < and == to be consistent with the standard algorithms, but it works like this as long as Elem has <= defined for it. Anyway, it can be used like this:
std::pair<int, int> intervals[]{
{11, 20}, {31, 40}, {51, 60}, {71, 80}, {91, 100}
};
const int num = 15;
std::cout << in_any_interval(std::begin(intervals), std::end(intervals), num);
There's a live example here.
The first one is easy. You just need to apply the modulo operator to your num value:
if ( ( num % 10 ) == 0)
Since C++ is evaluating every number that is not 0 as true, you could also write:
if ( ! ( num % 10 ) ) // Does not have a residue when divided by 10
For the second one, I think this is cleaner to understand:
The pattern repeats every 20, so you can calculate modulo 20.
All elements you want will be in a row except the ones that are dividable by 20.
To get those too, just use num-1 or better num+19 to avoid dealing with negative numbers.
if ( ( ( num + 19 ) % 20 ) > 9 )
This is assuming the pattern repeats forever, so for 111-120 it would apply again, and so on. Otherwise you need to limit the numbers to 100:
if ( ( ( ( num + 19 ) % 20 ) > 9 ) && ( num <= 100 ) )
With a couple of good comments in the code, it can be written quite concisely and readably.
// Check if it's a multiple of 10
if (num % 10 == 0) { ... }
// Check for whether tens digit is zero or even (1-10, 21-30, ...)
if ((num / 10) % 2 == 0) { ... }
else { ... }
You basically explained the answer yourself, but here's the code just in case.
if((x % 10) == 0) {
// Do this
}
if((x > 10 && x < 21) || (x > 30 && x < 41) || (x > 50 && x < 61) || (x > 70 && x < 81) || (x > 90 && x < 101)) {
// Do this
}
You might be overthinking this.
if (x % 10)
{
.. code for 1..9 ..
} else
{
.. code for 0, 10, 20 etc.
}
The first line if (x % 10) works because (a) a value that is a multiple of 10 calculates as '0', other numbers result in their remainer, (b) a value of 0 in an if is considered false, any other value is true.
Edit:
To toggle back-and-forth in twenties, use the same trick. This time, the pivotal number is 10:
if (((x-1)/10) & 1)
{
.. code for 10, 30, ..
} else
{
.. code for 20, 40, etc.
}
x/10 returns any number from 0 to 9 as 0, 10 to 19 as 1 and so on. Testing on even or odd -- the & 1 -- tells you if it's even or odd. Since your ranges are actually "11 to 20", subtract 1 before testing.
A plea for readability
While you already have some good answers, I would like to recommend a programming technique that will make your code more readable for some future reader - that can be you in six months, a colleague asked to perform a code review, your successor, ...
This is to wrap any "clever" statements into a function that shows exactly (with its name) what it is doing. While there is a miniscule impact on performance (from "function calling overhead") this is truly negligible in a game situation like this.
Along the way you can sanitize your inputs - for example, test for "illegal" values. Thus you might end up with code like this - see how much more readable it is? The "helper functions" can be hidden away somewhere (the don't need to be in the main module: it is clear from their name what they do):
#include <stdio.h>
enum {NO, YES, WINNER};
enum {OUT_OF_RANGE=-1, ODD, EVEN};
int notInRange(int square) {
return(square < 1 || square > 100)?YES:NO;
}
int isEndOfRow(int square) {
if (notInRange(square)) return OUT_OF_RANGE;
if (square == 100) return WINNER; // I am making this up...
return (square % 10 == 0)? YES:NO;
}
int rowType(unsigned int square) {
// return 1 if square is in odd row (going to the right)
// and 0 if square is in even row (going to the left)
if (notInRange(square)) return OUT_OF_RANGE; // trap this error
int rowNum = (square - 1) / 10;
return (rowNum % 2 == 0) ? ODD:EVEN; // return 0 (ODD) for 1-10, 21-30 etc.
// and 1 (EVEN) for 11-20, 31-40, ...
}
int main(void) {
int a = 12;
int rt;
rt = rowType(a); // this replaces your obscure if statement
// and here is how you handle the possible return values:
switch(rt) {
case ODD:
printf("It is an odd row\n");
break;
case EVEN:
printf("It is an even row\n");
break;
case OUT_OF_RANGE:
printf("It is out of range\n");
break;
default:
printf("Unexpected return value from rowType!\n");
}
if(isEndOfRow(10)==YES) printf("10 is at the end of a row\n");
if(isEndOfRow(100)==WINNER) printf("We have a winner!\n");
}
For the first one:
if (x % 10 == 0)
will apply to:
10, 20, 30, .. 100 .. 1000 ...
For the second one:
if (((x-1) / 10) % 2 == 1)
will apply for:
11-20, 31-40, 51-60, ..
We basically first do x-1 to get:
10-19, 30-39, 50-59, ..
Then we divide them by 10 to get:
1, 3, 5, ..
So we check if this result is odd.
As others have pointed out, making the conditions more concise won't speed up the compilation or the execution, and it doesn't necessarily help with readability either.
It can help in making your program more flexible, in case you decide later that you want a toddler's version of the game on a 6 x 6 board, or an advanced version (that you can play all night long) on a 40 x 50 board.
So I would code it as follows:
// What is the size of the game board?
#define ROWS 10
#define COLUMNS 10
// The numbers of the squares go from 1 (bottom-left) to (ROWS * COLUMNS)
// (top-left if ROWS is even, or top-right if ROWS is odd)
#define firstSquare 1
#define lastSquare (ROWS * COLUMNS)
// We haven't started until we roll the die and move onto the first square,
// so there is an imaginary 'square zero'
#define notStarted(num) (num == 0)
// and we only win when we land exactly on the last square
#define finished(num) (num == lastSquare)
#define overShot(num) (num > lastSquare)
// We will number our rows from 1 to ROWS, and our columns from 1 to COLUMNS
// (apologies to C fanatics who believe the world should be zero-based, which would
// have simplified these expressions)
#define getRow(num) (((num - 1) / COLUMNS) + 1)
#define getCol(num) (((num - 1) % COLUMNS) + 1)
// What direction are we moving in?
// On rows 1, 3, 5, etc. we go from left to right
#define isLeftToRightRow(num) ((getRow(num) % 2) == 1)
// On rows 2, 4, 6, etc. we go from right to left
#define isRightToLeftRow(num) ((getRow(num) % 2) == 0)
// Are we on the last square in the row?
#define isLastInRow(num) (getCol(num) == COLUMNS)
// And finally we can get onto the code
if (notStarted(mySquare))
{
// Some code for when we haven't got our piece on the board yet
}
else
{
if (isLastInRow(mySquare))
{
// Some code for when we're on the last square in a row
}
if (isRightToLeftRow(mySquare))
{
// Some code for when we're travelling from right to left
}
else
{
// Some code for when we're travelling from left to right
}
}
Yes, it's verbose, but it makes it clear exactly what's happening on the game board.
If I was developing this game to display on a phone or tablet, I'd make ROWS and COLUMNS variables instead of constants, so they can be set dynamically (at the start of a game) to match the screen size and orientation.
I'd also allow the screen orientation to be changed at any time, mid-game - all you need to do is switch the values of ROWS and COLUMNS, while leaving everything else (the current square number that each player is on, and the start/end squares of all the snakes and ladders) unchanged.
Then you 'just' have to draw the board nicely, and write code for your animations (I assume that was the purpose of your if statements) ...
You can try the following:
// Multiple of 10
if ((num % 10) == 0)
{
// Do something
}
else if (((num / 10) % 2) != 0)
{
// 11-20, 31-40, 51-60, 71-80, 91-100
}
else
{
// Other case
}
I know that this question has so many answers, but I will thrown mine here anyway...
Taken from Steve McConnell's Code Complete, 2nd Edition:
"Stair-Step Access Tables:
Yet another kind of table access is the stair-step method. This access method isn’t as direct as an index structure, but it doesn’t waste as much data space. The general idea of stair-step structures, illustrated in Figure 18-5, is that entries in a table are valid for ranges of data rather than for distinct data points.
Figure 18-5 The stair-step approach categorizes each entry by determining the level at which it hits a “staircase.” The “step” it hits determines its category.
For example, if you’re writing a grading program, the “B” entry range might be from 75 percent to 90 percent. Here’s a range of grades you might have to program someday:
To use the stair-step method, you put the upper end of each range into a table and then write a loop to check a score against the upper end of each range. When you find the point at which the score first exceeds the top of a range, you know what the grade is. With the stair-step technique, you have to be careful to handle the endpoints of the ranges properly. Here’s the code in Visual Basic that assigns grades to a group of students based on this example:
Although this is a simple example, you can easily generalize it to handle multiple students, multiple grading schemes (for example, different grades for different point levels on different assignments), and changes in the grading scheme."
Code Complete, 2nd Edition, pages 426 - 428 (Chapter 18).

Checking Who Won Tic Tac Toe More Efficient C++

I'm writing a Tic Tac Toe Game and I would like to know how I can make an efficient function to check who won. A two dimensional array congaing X's, O's, or blank spaces represents the board.
char CheckWin(const char board[][NUM_COLS], int& sum) // tic tac toe board - IN
{
char tmp;
int lcv;
tmp = ' ';
if (sum == 9)
{
return 'T';
}
else if (sum != 9)
{
if (((tmp = board[1][1]) != ' ' && board[0][0] == tmp && board[2][2] == tmp) || (board[2][0] == tmp && board[0][2] == tmp))
{
return tmp;
}
for (lcv = 0; lcv < 3; lcv++)
{
if ((tmp = board[lcv][0]) != ' ' && board[lcv][1] == tmp && board[lcv][2] == tmp)
{
return tmp;
}
else if ((tmp = board[lcv][0]) != ' ' && board[lcv][1] == tmp && board[lcv][2] == tmp)
{
return tmp;
}
}
}
return 'N';
}
Besides doing something similar to this over and over again, how could I check who won and return an X if X has won, an O if O has one, a T if it's a tie, and N if no one has one yet. Thanks in advance. I'm trying to get familiar with C++ and programming in general still.
EDIT: I just went with the simple method, but I somehow messed it up, anybody know how? It looks like it's not return anything because when I call it in the main after a player picks a row and column(that's working fine), it doesn't output anything
You could convert the array into two nine-bit values, one for the O positions and one for the X position, and a count of blank spaces:
x_mask = 0
y_mask = 0
empty_count = 0
mask = 1
for each square
if x then x_mask |= mask
if y then y_mask |= mask
if empty then empty_count++
mask <<= 1
Then compare the x_mask and y_mask against the eight possible winning combinations:
for each player
for each winning combination
if player_mask & winning_mask == winning_mask then player has won
and then handle the cases neither player has won:
if neither player won
if empty_count == 0
its a tie
else
moves still available
A simple "structured" approach
If you think of the board as:
A B C
D E F
G H I
Then one minimal selection of boxes that any winning layout must touch would be:
A B C
D
G
You can conceive the movement from any of these locations in a winning line in terms of a shift of 0, 1 or -1 positions in each of the X and Y directions. We can list the movements that you'd need to check:
A: (++x) (++x, ++y) (++y)
B: (++y)
C: (++y) (--x, ++y)
D: (++x)
E: (++x)
In C++, you can create a list/vector of the x/y coordinates of the starting points and the +/-/0 x/y movement deltas shown above, then use three nested loops to evaluate each line across the board.
This is considerably more work than just hardcoding the two loops over x and y coordinates and the two diagonals (below), but it's a more algorithmic approach that might appeal intellectually: more like what you might have to do if you were handling a much bigger board.
Obvious brute force approach
For the record, that simpler approach would look like this:
int x;
for (row = 0; row < 3; ++row)
if ((x = board[row][0]) != Empty &&
board[row][1] == x && board[row][2] == x)
return x;
// similar loop for columns...
...
// hardcode diagonals...
if ((x = board[1][1]) != Empty &&
(board[0][0] == x && board[2][2] == x ||
board[2][0] == x && board[0][2] == x))
return x
I suppose you could assign each winning board possibility a number (basically a hash value) and then check if the current board matches any of the values in the table by generating its hash value. On the other hand, I wouldn't suggest spending too much time trying to make the CheckWin function super-efficient. Unless it's being called millions of times or something and needs to be really fast, spend your time on something else--it probably won't be a bottleneck.