c++ - Cellular automaton doesn't make new cells -

i'm trying make program able create every kind of cellular automatons, such conway's game of life , else too.

the graphic implementation works already, wouldn't waste time (especially uses allegro libraries), functions counts cells, doesn't work properly.

that's have @ moment. (the code in order, break commentary make clear you)

pre-definitions:

#define fldwidth 110  #define fldheight 140 

a structure graphics:

typedef struct tiles {         unsigned char red, green, blue; }tiles; 

two predefined structures: rgb code of alive , dead test cell.

const tiles test_alive = {200,0,0}; const tiles test_dead = {100,0,0}; 

a function checks color equality of structure variable , constant structure.

bool equality(tiles& a, const tiles& b)  {     if (a.red == b.red && a.green == b.green && a.blue == b.blue)     {         return true;     } else {         return false;     } } 

the main function. gets 2 arrays of structures (first 1 current round, second 1 counting happens; in round loop, after counting, b array copied array); when started, following steps every structures: counts, how many living cells has in neighborhood (if living cell, starts -1 avoid counting neighbours, otherwise start 0 regularly), if not living test cell (but else) , has 5 neighbours, becomes living test cell; if living test cell , has 2 neighbours, becomes dead cell.

void test(tiles arra[fldwidth][fldheight], tiles arrb[fldwidth][fldheight]) {     int a,b,i,j,counter;      (j=1;j<fldheight-1;j++)     {         (i=1;i<fldwidth-1;i++)         {         if (equality(arra[i][j], test_alive) == true)         {         counter = -1;         } else {             counter = 0;         }         (b=j-1;b<j+1;b++)         {             (a=i-1;a<i+1;a++)             {                 if (equality(arra[a][b], test_alive) == true)                 {                     counter+=1;                 }             }         }         arrb[i][j] = arra[i][j];             if (equality(arra[i][j], test_alive) == false && counter == 5)             {                 arrb[i][j] = test_alive;             }              if (equality(arra[i][j], test_alive) == true && counter == 2)             {                 arrb[i][j] = test_dead;             }         }     } } 

the problem when counting begins, every living cell becomes dead in first round , disappear, without becoming dead cell (which darker red colour obviously), , happens every "counter == xy" check.

i've got tips, have no idea, why doesn't work. have logic failure? because can't see mistake, though there.

edit:

arra[fldwidth][fldheight] 

is replaced by

arra[i][j] 

and

arrb[i][j] = arra[i][j];

is added. stays put.

why access arra[fldwidth][fldheight] equality checks? outside of array, 1 element behind last element in array! want access arra[i][j].

and unless arrb starts copy of arra, want add arrb[i][j] = arra[i][j]; in front of 2 equality checks. way if cell doesn't meet of 2 state change rules, keep current state.

edit:

you need let loop run between i-1 , i+1, should be: for (a = i-1; <= i+1; a++), same b!