This program prints tree in zig zag fashion

zigzag_iter.c

void zigzag(Node * root){

        stack s1, s2;
        s1.top = -1;
        s2.top = -1;
        if(root == NULL ) return;
        push(&s1, root);

        while(!is_empty(s1) || !is_empty(s2)){
        printf("\n");
        while(!is_empty(s1)){
                Node * temp = pop(&s1);
                printf("%d " , temp->value);
                if(temp->right)
                        push(&s2, temp->right);
                if(temp->left)
                        push(&s2, temp->left);
        }
        printf("\n");
        while(!is_empty(s2)){
                Node * temp = pop(&s2);
                printf("%d " , temp->value);
                if(temp->left)
                        push(&s1, temp->left);
                if(temp->right)
                        push(&s1, temp->right);
        }
        }
}