Edit in JSFiddle

$('#select_all').click(function() {
    $('*').val('I am a input element');
});

$('#select_id').click(function() {
    $('#fooId').val('My id is fooId');
});

$('#select_class').click(function() {
    $('.fooClass').val('My class is fooClass');
});

$('#select_fourth').click(function() {
    $('input:eq(3)').val('I am fourth input');
});

$('#reset').click(function() {
    $('input').val('Yet another input');
});

Input 1 <input value="Yet another input"><br/><br/>
Input 2 <input id="fooId" value="Yet another input"><br/><br/>
Input 3 <input class="fooClass" value="Yet another input"><br/><br/>
Input 4 <input value="Yet another input"><br/><br/>
Input 5 <input value="Yet another input"><br/><br/>  
<br/>

<button id="select_all"> Select all</button> 
<button id="select_id"> Select by id</button>
<button id="select_class"> Select by class</button>
<button id="select_fourth"> Select fourth input</button>
<button id="reset"> Reset </button>