ViewController.swift

import UIKit

class ViewController: UIViewController {
    
    var count: Int = 0 {
        didSet {
            countLabel.text = "\(count)"
        }
    }
    
    let plusButton: UIButton = {
        let button = UIButton()
        button.setTitle("+", for: .normal)
        button.setTitleColor(.systemBlue, for: .normal)
        button.titleLabel?.font = UIFont.systemFont(ofSize: 120)
        button.tag = 1
        return button
    }()
    
    let minusButton: UIButton = {
        let button = UIButton()
        button.setTitle("-", for: .normal)
        button.setTitleColor(.systemBlue, for: .normal)
        button.titleLabel?.font = UIFont.systemFont(ofSize: 120)
        button.tag = 2
        return button
    }()
    
    let countLabel: UILabel = {
        let label = UILabel()
        label.text = "0"
        label.textColor = .black
        label.font = UIFont.systemFont(ofSize: 120)
        return label
    }()
    
    let mainStack: UIStackView = {
        let stack = UIStackView()
        stack.axis = .vertical
        stack.alignment = .center
        return stack
    }()
    
    let buttonStack: UIStackView = {
        let stack = UIStackView()
        stack.axis = .horizontal
        stack.distribution = .fillEqually
        stack.spacing = 8
        return stack
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupUI()
    }

    func setupUI() {
        [plusButton, minusButton, countLabel, mainStack, buttonStack].forEach {
            $0.translatesAutoresizingMaskIntoConstraints = false
        }
        
        buttonStack.addArrangedSubview(minusButton)
        buttonStack.addArrangedSubview(plusButton)
        view.addSubview(buttonStack)
        
        mainStack.addArrangedSubview(countLabel)
        mainStack.addArrangedSubview(buttonStack)
        view.addSubview(mainStack)
        
        NSLayoutConstraint.activate([
            mainStack.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            mainStack.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
        
        plusButton.addTarget(self, action: #selector(counter), for: .touchUpInside)
        minusButton.addTarget(self, action: #selector(counter), for: .touchUpInside)
    }
    
    @objc func counter(_ sender: UIButton) {
        if sender.tag == 1 {
            count += 1
        }
        
        if sender.tag == 2 && count > 0 {
            count -= 1
        }
    }
}