Cant convert int to string in c#

Here is my code:

public class checklevelcheckskill : MonoBehaviour {

    public string PlayerSKillPointsS;
    public int RequiredSkillLevelForUpgrade;
    public int PlayerSkillPointsInInt;

    //BUttons and Menus
    public GameObject SkillPointsWarningMenu;
    //Written Variables

	// Use this for initialization
	public void Start ()
    {
        RequiredSkillLevelForUpgrade = 0;
        SkillPointsWarningMenu.active = false;
	}
	
	// Update is called once per frame
	void Update ()
    {
        PlayerPrefs.GetString("PlayerSkillPoints");
        PlayerSKillPointsS = PlayerPrefs.GetString("PlayerSkillPoints");
        PlayerSkillPointsInInt = PlayerSKillPointsS;
    }

}

Im getting this error: Cannot implicitly convert type ‘string’ to ‘int’ And when I changed my script to this,

public class checklevelcheckskill : MonoBehaviour {

    public string PlayerSKillPointsS;
    public int RequiredSkillLevelForUpgrade;
    public int PlayerSkillPointsInInt;

    //BUttons and Menus
    public GameObject SkillPointsWarningMenu;
    //Written Variables

	// Use this for initialization
	public void Start ()
    {
        RequiredSkillLevelForUpgrade = 0;
        SkillPointsWarningMenu.active = false;
	}
	
	// Update is called once per frame
	void Update ()
    {
        PlayerPrefs.GetString("PlayerSkillPoints");
        PlayerSKillPointsS = PlayerPrefs.GetString("PlayerSkillPoints");
        PlayerSkillPointsInInt.ToString() = PlayerSKillPointsS;
    }

}

Now Im getting this error: The left-hand side of an assignment must be a variable, property or indexer

I just want first variable to be equal to second one. PlayerSkillPointsInInt = PlayerSKillPointsS;

Are there anybody knows how to solve this problem? Thanks For Your Help.

Your title says convert int to string, which is done trivially using the ToString() method.
However, your question is actually about converting string to int, which must be done slightly differently since not every string can be represented as an int. Try this :

int.TryParse(PlayerSKillPointsS, out PlayerSkillPointsInInt);