<input type="text" id="n1"/><br/><br/>
        <input type="text" id="n2"/><br/><br/>

 <button onclick="calc();">=</button>
        <input type="text" id="result"/>

THIS IS FOR JS

 function calc()
            {
                var n1 = parseFloat(document.getElementById('n1').value);
                var n2 = parseFloat(document.getElementById('n2').value);

 document.getElementById('result').value = n1+n2;

}