Question

why do i get this syntax error?

for example: i have these two classes:

class Maze
{
private:
    int row, col;
    cell **arr;
public:
    Maze(int r = 0, int c = 0)
    {
        this->row = r; this->col = c;
        arr = new cell*[row];
        for (int i = 0; i < row; i++)
            arr[i] = new cell[col];
    }

};

class cell
{
private:
    bool visited;
    bool up, down, right, left;
    int x, y;
    int px, py;
    char status;
public:
    cell() {
        up = down = right = left = 0;
        x = y = 0;
        status = ' ';
    }
    bool getUp() { return up; }
    bool getDown() { return down; }
    bool getRight() { return right;  }
    bool getLeft() { return left; }
    bool getvisited() { return visited; }
    void setUp(bool b) { up = b; }
    void setDown(bool b) { down = b; }
    void setRight(bool b) { right = b; }
    void setLeft(bool b) { left = b; }

    void setvisited(bool b=0) { visited = b; }
    void setstatus(char s = ' ') { status = s; }
    char getStatus() { return status; }

};

and in main:

int main(){

Maze m (5,5);

m[1][1].setDown(false); //here error

}

Answer 1

setDown() method is a public function of class cell. But instance m is an object of class Maze. Hence object m can't call member function of another object. Using arr member field of Maze class, setDown method can be called. But it can't be called from main function, as arr member field is private. A proper member function inside Maze class should call the setDown() method using the arr field.

Thus the program should look like:

#include <iostream>

class cell
{
private:
bool visited;
bool up, down, right, left;
int x, y;
int px, py;
char status;
public:
cell() {
up = down = right = left = 0;
x = y = 0;
status = ' ';
}
bool getUp() { return up; }
bool getDown() { return down; }
bool getRight() { return right; }
bool getLeft() { return left; }
bool getvisited() { return visited; }
void setUp(bool b) { up = b; }
void setDown(bool b) { down = b; }
void setRight(bool b) { right = b; }
void setLeft(bool b) { left = b; }

void setvisited(bool b=0) { visited = b; }
void setstatus(char s = ' ') { status = s; }
char getStatus() { return status; }

};

class Maze
{
private:
int row, col;
cell ***arr;
public:
Maze(int r = 0, int c = 0)
{
this->row = r; this->col = c;
arr = new cell**[row];
for (int i = 0; i < row; i++)
arr[i] = new cell*[col];
for (int i = 0; i < row; i++)
for(int j=0; j< col; j++)
arr[i][j] = new cell();
}
void decreaseCell()
{
arr[1][1]->setDown(false);
}
};

int main()
{
Maze m(5,5);
m.decreaseCell();
}