[백준] 10828번 : 스택 - C#

https://www.acmicpc.net/problem/10828

using System;
using System.Text;

class Stack {
    int si;
    int[] stack;
    
    public Stack(int num){
        stack = new int[num];
        si=0;
    }
    public void push(int num) {
        stack[si] = num;
		si++;
    }
    public int pop() {
		if(si == 0) return -1;
		else {
			int ans = stack[si - 1];
			stack[si - 1] = 0;
			si--;
			return ans;
		}
	}
	public int size() {
		return si;
	}
	public int empty() {
		if(si == 0) return 1;
		else return 0;
	}
	public int top() {
		if(si == 0) return -1;
		else return stack[si - 1];
	}
}

class Program
{
    static void Main() {
        string st=Console.ReadLine();
        StringBuilder sb = new StringBuilder();
        int n=int.Parse(st);
        Stack t=new Stack(n);
        
        for(int i=0;i<n;i++){
            string[] st1=Console.ReadLine().Split();
            
            switch (st1[0]) {
			case "push":
				t.push(int.Parse(st1[1]));
				break;
			case "pop":
				sb.Append(t.pop()+"\n");
				break;
			case "size":
				sb.Append(t.size()+"\n");
				break;
			case "empty":
				sb.Append(t.empty()+"\n");
				break;
			case "top":
				sb.Append(t.top()+"\n");
				break;
			}
        }
        Console.WriteLine(sb.ToString());
    }
}