void printtictactoe(char horizchar, char vertchar)
{
int i,j;
int scale = 5;
 for(j=0; j<3; j++) {
 for (i = 0; i < scale; i++)
 printf("%*c%*c\\", scale+1, vertchar, scale+1, vertchar);
 if (j < 2) 
 for (i = 0; i < (scale * 3)+2; i++)
 printf("%c", horizchar);
 printf("\\");
 }
}
I left out many braces because of the layout issues with this website. There is a scale factor you can set to the desired size of the board cells!