ios除去可变字符串中的某些字符

//除去字符串中的“111@”

NSMutableString *str = [[NSMutableString alloc]initWithFormat:@"111@sudhqu111@lgkokge"];

    while ([str rangeOfString:@"111@"].length>0)

    {

        [str deleteCharactersInRange:[str rangeOfString:@"111@"]];

    }