I've got a minor problem.
I'm using multidimensional-vectors and I want to insert some values to it at a given position. I'm making a sudoku in wxWidgets and i'm getting the tiles the player have put in and wanting to store them in my mVector.
The mVector looks like this.
vector< vector<string> > board{9, vector<string>(9)};
And at first i've added values just like this.
board[row][col] = value;
"value" is a string and row/col are ints.
Is this a legit way of adding values to the mVector? I'm asking this because when I update the board, by doing this above, I for some reason can't run my other functions where i'm solving the board, giving a hint to the board and so on. Before i store the new values to it all the functions works correkt. Do I maby need to use some other type of build in functions for the vector like insert, push_back or something instead?
Since you declared the vector as size 9x9, yes that is a valid way of assigning values.
Otherwise you could declare the board as
vector<vector<string>> board;
Then fill it with
for (int i = 0; i < 9; ++i)
{
vector<string> row;
for (int j = 0; j < 9; ++j)
{
row.push_back(value); // where value is whatever you want
}
board.push_back(row);
}
But again, once the board is of size 9x9, you can simply assign a value at any cell for example
board[2][4] = "hello";
Working example
Related
So I'm very new to c++, studying it at present and have a piece of work to do that's stumping me. You guys are the first port of call.
I need to make what is essentially a 2d array of objects. The header file includes Cell objects for rows, columns and blocks. The idea that I have a 9x9 array of objects, with relevant pointers based on column, row and internal 3x3 block therein. What I'm stuck on is that the below line fills out the 9x9 but how am I pointing to each Cell?
Or is that in something separate and this is all I need to do for just setting up that grid??
void SudokuPuzzle::InitialiseGrid()
{
for (int row = 0; row < 9; row++)
{
for (int column = 0; column < 9; column++)
{
m_gridRows[row].SetCell(column, new SudokuSquare());
// have the cell point to both it's position in the column and block
}
}
}
Maybe try to create the 2d array of the Type "SudokuSquare".
SudokuSquare sSquare [9][9];
So you can acces any object by
sSquare[row][column];
If your array is fixed size e.g. 3x3 just use std::array:
#include <array>
using std::array;
int main()
{
array<array<int, 3>, 3> sudoku_squares{};
sudoku_squares[0][1] = 1; // sets cell at first row, second column to 1
return 0;
}
In your case you can store 9 of those 3x3 arrays in another array or just use 9x9 array and you don't need to use any pointers. I used int in my example but you can store SudokuSquare exactly the same way.
I am having a problem in swapping two rows in a matrix that is a 2D-dynamic array. I wanted to know if there is a function to use directly or if there is none I would like to know how to make one. Thanks in advance.
Here is how I made the dynamic array:
int **ptrMatrix = new int*[row];
for (int i = 0; i < row; i++)
ptrMatrix[i] = new int[column];
I found the solution ... it is done simply by making a temporary variable (X) and appling the following code
for (int i=0;i<columns;i++)
{
X=matrix[row1-1][i];
matrix[row1-1][i]=matrix[row2-1][i];
matrix[row2-1][i]=X;
}
I have a general question. Hopefully, one of you has a good approach to solve my problem. How can I initialize an empty vector?
As far as I read, one has to know the size of an array at compiling time, though for vectors it is different. Vectors are stored in the heap (e.g. here: std::vector versus std::array in C++)
In my program I want to let the client decide how accurate interpolation is going to be done. That's why I want to use vectors.
The problem is: For reasons of clear arrangement I want to write two methods:
one method for calculating the coefficients of an vector and
one method which is providing the coefficients to other functions.
Thus, I want to declare my vector as global and empty like
vector<vector<double>> vector1;
vector<vector<double>> vector2;
However, in the method where I determine the coefficients I cannot use
//vector containing coefficients for interpolation
/*vector<vector<double>>*/ vector1 (4, vector<double>(nn - 1));
for (int ii = 0; ii < nn - 1; ii++) {vector1[ii][0] = ...;
}
"nn" will be given by the client when running the program. So my question is how can I initialize an empty vector? Any ideas are appreciated!
Note please, if I call another function which by its definition gives back a vector as a return value I can write
vector2= OneClass.OneMethod(SomeInputVector);
where OneClass is an object of a class and OneMethod is a method in the class OneClass.
Note also, when I remove the comment /**/ in front of the vector, it is not global any more and throws me an error when trying to get access to the coefficients.
Use resize:
vector1.resize(4, vector<double>(nn - 1));
Use resize() function as follows:
vector<vector<double>> v;
int f(int nn){
v.resize(4);
for(int i = 0; i < 4; i++){
v[i].resize(nn - 1);
}
}
It look to me that you're actually asking how to add items to your global vector. If so this might help:
//vector containing coefficients for interpolation
for (int i = 0; i < 4; ++i)
vector1.push_back(vector<double>(nn - 1));
for (int ii = 0; ii < nn - 1; ii++)
{
vector1[ii][0] = ...;
}
Unsure if it is what you want, but assign could be interesting :
vector<vector<double>> vector1; // initialises an empty vector
// later in the code :
vector<double> v(nn -1, 0.); // creates a local vector of size 100 initialized with 0.
vector1.assign(4, v); // vector1 is now a vector of 4 vectors of 100 double (currently all 0.)
I'm pretty new to C++ and got an assignment to make a matrix using only STL containers. I've used a vector (rows) of vectors (columns). The problem I'm having is in the 'write' operation - for which I may only use an iterator-based implementation. Problem is, quite simply: it writes nothing.
I've tested with a matrix filled with different values, and while the iterator ends up on exactly the right spot, it doesn't change the value.
Here's my code:
void write(matrix mat, int row, int col, int input)
{
assert(row>=0 && col>=0);
assert(row<=mat.R && col<=mat.C);
//I set up the iterators.
vector<vector<int> >::iterator rowit;
vector<int>::iterator colit;
rowit = mat.rows.begin();
//I go to the row.
for(int i = 0; i<row-1; ++i)
{
++rowit;
}
colit = rowit->begin();
//I go to the column.
for(int j = 0; j<col-1; ++j)
{
++colit;
}
*colit = input; //Does nothing.
}
What am I overlooking?
Thanks.
matrix mat is a parameter by value, it copies the matrix and hence you are writing to a copy.
You should pass the matrix by reference instead, like matrix & mat.
But wait... You are passing the matrix every time as the first parameter, this is a bad sign!
This usually indicates that the parameter should be turned into an object on which you can run the methods; that way, you don't need to pass the parameter at all. So, create a Matrix class instead.
Please note that there is std::vector::operator[].
So, you could just do it like this:
void write(matrix & mat, int row, int col, int input)
{
assert(row>=0 && col>=0);
assert(row<=mat.R && col<=mat.C);
mat[row][col] = input;
}
I'm having a problem with my looping over a vector, and deleting values from another vector sometimes crashes my program. I have this vector of int's to keep track of which elements should be removed.
std::vector<int> trEn;
Then I loop through this vector:
struct enemyStruct {
float x, y, health, mhealth, speed, turnspeed;
double angle, tangle;
};
std::vector<enemyStruct> enemies;
The loop looks like this:
for ( unsigned int i = 0; i < bullets.size(); i++ ) {
for ( unsigned int j = 0; j < enemies.size(); j++ ) {
if ( bullets[i].x > enemies[j].x-10 && bullets[i].x < enemies[j].x+10 && bullets[i].y > enemies[j].y-10 && bullets[i].y < enemies[j].y+10 )
{
enemies[j].health-=bullets[i].dmg;
if(enemies[j].health<=0){trEn.push_back(j);break;}
}
}
}
The bullets vector is just another vector similar to the enemies vector, but with bullets in it. That one does not seem to be the problem. All this code works well, but when it comes to actually delete the items in my enemies vector the program sometimes crashes.
std::reverse( trEn.begin(), trEn.end() );
for ( unsigned int g = 0; g < trEn.size(); g++ ) {
unsigned int atmp = trEn.at(g);
if(atmp<=enemies.size()&&atmp>=0)enemies.erase(enemies.begin()+atmp,enemies.begin()+atmp+1);
} trEn.clear();
First I reverse the vector of int´s so that it will go from back to front. If i did´nt do this all values after trEn[0] would be invalid.
This is the loop which gives me a crash, but only sometimes. What I´m trying to do is a top-down shooter game, and it seems that when lots of things should be removed at the same time it just crashes. Please help me with this!
Just ask if I was unclear or if there is anything missing.
The only seemingly obvious thing would be:
if(atmp<=enemies.size() ...
Are you sure you do not mean (atmp < enemies.size()) here? Otherwise your code
enemies.erase(enemies.begin()+atmp, ...
will for sure produce some serious issues.
Your first code sample are two nested loops - you iterate over bullets and for each bullet you iterate over enemies adding enemy indices to trEn vector. What makes you think that contents of trEn are sorted in ascending order after that? For first bullet you can add index 3, and for the second index 2. You can even add same index for different bullets. Or am I missing something?