x = y = (size + 1) / 2;
   matrix[x][y]=1;                                                          //default of the matrix

   x1=y1=rand()%(size-1);                                                   //random selection of matrix position

   number= switch(rand() %4){
   case 0;
        matrix[x1][0]==1;
        break;
   case 1;
        matrix[size-1][y1]==1;
        break;
   case 2;
        matrix[0][y1]==1;
        break;
   case 3;
        matrix[x1][size-1]==1;
        break
   }