Solution Review: Implement Two Stacks Using One Array

namespace chapter_4
{
    //You can either divide array in two halves or start stacks at extreme ends.
    //We'll use the second technique to solve this problem. 
    //Top of Stack 1 starts from extreme left of array i.e top1 = 0;
    //Top of Stack 2 starts from extreme right of array i.e top2 = size - 1;
    class twoStacks
    {
        int size;
        int [] arr;
        int top1, top2;
        //Store top value indices of Stack 1 and Stack 2
        public twoStacks(int n)
        {
            size = n;
            arr = new int[size];
            top1 = -1;
            top2 = size;
        }
        //Insert Value in First Stack  
        public void push1(int value)
        {
            //Check for empty space and insert value if there's an empty space.
            if (top1 < top2 - 1)
            {
                arr[++top1] = value;
            }
        }
        //Insert Value in Second Stack  
        public void push2(int value)
        {
            //Check for empty space and insert value if there's an empty space.
            if (top1 < top2 - 1)
            {
                arr[--top2] = value;
            }
        }
        //Return and remove top Value from First Stack
        public int pop1()
        {
            //Get value from top1 index and increment it.
            if (top1 >= 0)
            {
                int val = arr[top1--];
                return val;
            }
            return -1;
        }
        //Return and remove top Value from Second Stack
        public int pop2()
        {
            //Get value from top2 index and increment it.
            if (top2 < size)
            {
                int val = arr[top2++];
                return val;
            }
            return -1;
        }
        static void Main(string[] args)
        {
            twoStacks tS = new twoStacks(5);
            tS.push1(11);
            tS.push1(3);
            tS.push1(7);
            tS.push2(1);
            tS.push2(9);
            Console.WriteLine(tS.pop1());
            Console.WriteLine(tS.pop2());
            Console.WriteLine(tS.pop2());
            Console.WriteLine(tS.pop2());
            Console.WriteLine(tS.pop1());
            
            return;
        }
    };
}