Space-Shooter-2D [Updated in GitHub on 22 Dec 2018]

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerController : MonoBehaviour {
    //speed of movement
    public float playerSpeed;
    //first element holds negative values -x,-y
    //second element holds positive values x,y
    public Vector2 []mapBorders;
    //shooting speed
    public float shootingSpeed;
    //is player shooting?
    public bool isShooting;
    //projectile object
    public GameObject projectile;

	// Use this for initialization
	void Start () {
        StartCoroutine(SpawnProjectile(shootingSpeed));
    }
	
	// Update is called once per frame
	void Update () {
        
    }

    //physical calculations
    void FixedUpdate()
    {
        PlayerMovement();
        PlayerShootingTimer();
    }

    //function that controls player's movement
    private void PlayerMovement()
    {
        //left movement
        if (Input.GetKey(KeyCode.LeftArrow) && transform.position.x > mapBorders[0].x)
        {
            transform.Translate(-playerSpeed, 0, 0);
        }

        //right movement
        if (Input.GetKey(KeyCode.RightArrow) && transform.position.x < mapBorders[1].x)
        {
            transform.Translate(playerSpeed, 0, 0);
        }

        //down movement
        if (Input.GetKey(KeyCode.DownArrow) && transform.position.y > mapBorders[0].y)
        {
            transform.Translate(0, -playerSpeed, 0);
        }

        //up movement
        if (Input.GetKey(KeyCode.UpArrow) && transform.position.y < mapBorders[1].y)
        {
            transform.Translate(0, playerSpeed, 0);
        }
    }
    
    //function that controls player's shooting time
    private void PlayerShootingTimer()
    {
        if (Input.GetKey(KeyCode.LeftControl))
        {
            isShooting = true;
        }
        else if (Input.GetKeyUp(KeyCode.LeftControl))
        {
            isShooting = false;
        }
    }
    
    //function spawning projectile
    IEnumerator SpawnProjectile(float shootingSpeed)
    {
        while (true)
        {
            if (isShooting == true)
            {
                Instantiate(projectile, new Vector3(transform.position.x, transform.position.y + 1f, transform.position.z), Quaternion.identity);
                yield return new WaitForSeconds(shootingSpeed);
            }
            else
            {
                yield return null;
            }
        }
    }
}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ProjectileController : MonoBehaviour {
    //projectile transform speed
    public float transformSpeed;
    public Vector2[] mapBorders;
    public GameObject ExplosionEffect;

    // Use this for initialization
    void Start () {
        mapBorders = GameObject.Find("Player").GetComponent<PlayerController>().mapBorders;
        GameObject.Find("GameController").GetComponent<SoundController>().isProjectileFired = true;
    }
	
	// Update is called once per frame
	void Update () {
		
	}

    //fixed frame
    private void FixedUpdate()
    {
        TransformProjectile();

        //check if projectile should be destroyed or not
        if (transform.position.y >= mapBorders[1].y + 1f)
        {
            Destroy(gameObject);
        }
    }

    //projectile transform
    private void TransformProjectile()
    {
        transform.Translate(0, transformSpeed, 0);
    }

    private void OnTriggerEnter2D(Collider2D collision)
    {
        if (collision.gameObject.tag == "SquareEnemy")
        {
            GameObject.FindGameObjectWithTag("GameController").GetComponent<ScoreCalculator>().score += 100;
            Instantiate(ExplosionEffect, new Vector3(transform.position.x, transform.position.y + 2f, transform.position.z), Quaternion.identity);
            GameObject.Find("GameController").GetComponent<SoundController>().isSquareEnemyKilled = true;
            Debug.Log("Square enemy was hit by projectile!");
            Destroy(collision.gameObject);
            Destroy(gameObject);
        }
    }
}