<div id="slides">
<div id="content-main" name="content-main">
<div id="a">
<img src="img/example-slide-1.jpg" alt="1">
</div>
</div>
<div id="content-main" name="content-main">
<div id="b">
<img src="img/example-slide-2.jpg" alt="1">
</div>
</div>

</div>
<input id="p" type="button" value="add" onclick="add1();"/>
<input id="p" type="button" value="add33" onclick="clear();"/>

function add1(){//Add a div content-main
var obj=document.createElement("div");
obj.id="content-main";
obj.innerHTML='<div id="c">'+
'<img src="img/example-slide-3.jpg" alt="3">'+
'</div>';
$('#slides').append(obj);
}

function clear(){//Clear all divs and img under slides
var div1=document.getElementById("slides").getElementsByTagName("div");
for(var i=0;i<div1.length;i++){
div1[i].innerHTML='';
}
}

function ClearAllText(divInput){ //Empty div under the content of the text text box, reset
var txts = document.getElementById('divInput').getElementsByTagName("input");
for(var i=0;i<txts.length;i++)
{
if(txts[i].type=="text"){
txts[i].value =""; //The text to empty
}
}
var selects = document.getElementById('divInput').getElementsByTagName("select");
for(var i=0;i<selects.length;i++)
{
selects[i].options[0].selected = true; //Select the first term
}
}