<!-- https://arkenidar.com/web/editor.html -->
<!-- ------------------------------------------ -->
<!-- --------------contatore------------------- -->
<button id=num onclick="this.textContent++">0</button>
<style>
#num{ width: 50px; height: 50px; font-size: 40px; }
</style>
<!-- ---------------somma---------------------- -->
<!-- interfaccia grafica in HTML -->
<input type="number" id="x" placeholder="numero x">
<input type="number" id="y" placeholder="numero y">
<div>il risultato è: <span id="risultato">0</span></div>
<!-- logica software in JavaScript -->
<script>
x.oninput=calc; y.oninput=calc
x.value=0; y.value=0
function calc(){ risultato.textContent = parseFloat(x.value) + parseFloat(y.value) }
calc()
</script>
<!-- ------------------percentuale------------- -->
<p>
inputs:
<input type="number" id="numero" placeholder="numero in input">
<input type="number" id="percentuale" placeholder="percentuale">
</p>
<p>
percentuale applicata:
<span id="risultato"></span>
</p>
<script>
numero.oninput = applica
percentuale.oninput = applica
function applica() {
risultato.textContent=numero.value*percentuale.value/100
}
</script>