<form method="post" onsubmit="return checkform(this);">
                    <span class="ipt-search-box">
                    <input type="text" name="k"  value="{$search_key}" class="ipt-search"/>
                    <input type="submit" value="search" class="gr-icon" />
                    </span>
                    <a class="red-btn btn22 ml10" href="{:U('expert/Topic/add',array('gid'=>$gid,'expert_type'=>'submit'))}">submit</a>                    
                </form>

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
function checkform(v_form){
    if (getLength(v_form.k.value) == 0) {
        v_form.k.focus();
        ui.error('Please enter key words');
        return false;
    }

    return true;
}

</script>