<?php
$json = ' {
    "response": {
        "success": true,
        "groups": [
            {
                "gid": "4458711"
            },
            {
                "gid": "9538146"
            },
            {
                "gid": "11683421"
            },
            {
                "gid": "24781197"
            },
            {
                "gid": "25160263"
            },
            {
                "gid": "26301716"
            },
            {
                "gid": "29202157"
            },
            {
                "gid": "1111111"
            }
        ]

    }
}';

		$groupid = "1111111";
		//$url = "https://api.steampowered.com/ISteamUser/GetUserGroupList/v1/?key=APIKEYHERE&steamid=STEAMID64HERE";
	//	$result = file_get_contents($url);
		// Will dump a beauty json :)
		$pretty = json_decode($json);
		$s = $pretty->response->groups;
		foreach($s as $value)
		{
			echo $value->gid;
			if((int) $groupid  ==  $value->gid)
			{
				echo  "Found";
				echo "<br></br>";
			}else
			{
				echo  "Not found";	
				echo "<br></br>";
			}	
		}


?>

4458711Not found<br></br>9538146Not found<br></br>11683421Not found<br></br>24781197Not found<br></br>25160263Not found<br></br>26301716Not found<br></br>29202157Not found<br></br>1111111Found<br></br>