Logic Error in TicTacToe game - c++

Question

here's a simple logic error I can't quite wrap my head around:
Why does the following statement always equate to true?
if ( (grid[i][0] && grid[i][1] && grid[i][2]) == ('X' || 'x') ) return true;
It works flawlessly for
if ( (grid[i][0] && grid[i][1] && grid[i][2]) == ('X') return true;

Answer 1

Do it like this:
create a function to check a character of being x:
bool isX(char c)
{
return c == 'X' || c == 'x';
}
and the you can write:
if ( isX(grid[i][0]) && isX(grid[i][1]) && isX(grid[i][2]))
return true;

Answer 2

That's because the expressions
'X' || 'x'
and
grid[i][0] && grid[i][1] && grid[i][2]
use the || and && operators between non-zero integer-typed values (because char is an integer type) and so they both evaluate to true.
To translate into C++ (or almost any other somewhat similar language, for that matter) that you want characters x, y and z to be equal to either of the characters c and C, you must compute
(x == c || x == C) && (y == c || y == C) && (z == c || z == C)
so apply that to your problem.
More importantly though, learn about boolean operators and programming in general before you try to tackle C++.

Answer 3

In the first case, it returns true because none of the grid elements has the value of zero. The && operator produces 0 or 1, depending on the values that you pass.
In the second case, it does not work as expected either: you wouldn't get an 'X' by &&-ing values together.
The proper way of checking if three items are equal to 'X' or not would be as follows:
if (toupper(grid[i][0]) == 'X'
&& toupper(grid[i][1]) == 'X'
&& toupper(grid[i][2]) == 'X') {
return true;
}
To generalize the concept of "win" in TiCTacToe, write a function that returns true when a sequence of three items with a specific step in each direction holds a sequence of a given character, like this:
bool isWin(int r, int c, int dr, int dc, char ch) {
return toupper(grid[r+0*dr][c+0*dc] == ch
&& toupper(grid[r+1*dr][c+1*dc] == ch
&& toupper(grid[r+2*dr][c+2*dc] == ch;
}
bool isWin(char ch) {
return isWin(0,0,0,1,ch)
|| isWin(0,0,1,0,ch)
|| isWin(1,0,0,1,ch)
|| isWin(0,1,1,0,ch)
|| isWin(2,0,0,1,ch)
|| isWin(0,2,1,0,ch)
|| isWin(0,0,1,1,ch)
|| isWin(2,0,-1,1,ch);
}