Error CS1002

My Script is

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

public class panelscript : MonoBehaviour {

public GameObject Panel;
int counter

public void showhidePanel()
{
counter++;
if (counter % 2 == 1) {
Panel.gameObject.SetActive (false);
} else {
Panel.gameObject.SetActive (true);
}
}
}

and I don’t know how to fix it can anyone help?

You forgot to add ; after the counter

int counter

should be

int counter;

And if you will look on the error message you will see that it tell you that the semicolon or semi-colon (;) is missing.
Error cs1002 is missing semicolon

And double click on the error will bring you to the line with the missing semicolon