how to make html button do calculation code example

Example 1: how to create a simple calculator in html

<!DOCTYPE html>
<html lang="en">
<head>
<style>
.contain{
display: flex;
}
#display{
  width: 98%;
  
}
.mathButtons{
  width: 100px;
  height: 40px;
  background-color: rgb(0,0,0,0.3);
  color: white;
}
.mathButtons:hover{
  background-color: DodgerBlue;
  
  }
  #clearButton:hover{
    background-color: orangered;
  }
  #container{
  
    width: 430px;
    height: 300px;

    }
    
    
    .buttondigits{
      background-color:  black;
      color: white;
      height: 40px;
      width: 100px;
    }
    #clearButton{
      width: 100px;
      height: 40px;
      background-color: rgb(0,0,0,0.3);
      font-weight: bold;
    }
	.buttondigits:hover {
background-color: gray;
}

</style>
<title> standard calculator </title>
<meta charset="utf-8">
<link rel="stylesheet" href="cal.css"/>
</head>
<body>
  
     <div class="container">
	<fieldset id="container">
	  <form name="calculator">
<input type="text" id="display" name="display" readonly>
<br>
<br>
<br>
<div class="contain">
<input class="buttondigits" type="button" value="7" onclick="calculator.display.value += '7'">
<input class="buttondigits" type="button" value="8" onclick="calculator.display.value += '8'">
<input class="buttondigits" type="button" value="9" onclick="calculator.display.value += '9'">
<input class="mathButtons" type="button" value="+" onclick="calculator.display.value += '+'">
</div>

<div class="contain">
<input class="buttondigits" type="button" value="4" onclick="calculator.display.value += '4'">
<input class="buttondigits" type="button" value="5" onclick="calculator.display.value += '5'">
<input class="buttondigits" type="button" value="6" onclick="calculator.display.value += '6'">
<input class="mathButtons" type="button" value="-" onclick="calculator.display.value += '-'">
</div>

<div class="contain">
<input class="buttondigits" type="button" value="1" onclick="calculator.display.value += '1'">
<input class="buttondigits" type="button" value="2" onclick="calculator.display.value += '2'">
<input class="buttondigits" type="button" value="3" onclick="calculator.display.value += '3'">
<input class="mathButtons" type="button" value="*" onclick="calculator.display.value += '*'">
</div>

<div class="contain">
<input id="clearButton" class="button" type="button" value="C" onclick="calculator.display.value = ''">
<input class="buttondigits" type="button" value="0" onclick="calculator.display.value += '0'">
<input class= "mathButtons" type="button" value="=" onclick="calculator.display.value = eval(calculator.display.value)">
<input class="mathButtons" type="button" value="/" onclick="calculator.display.value += '/'">
</div>
</form> 
</fieldset>
</div>
</body>
</html>

Example 2: What is the code for a calculator

<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Calculator Made by Sanjith </title>
<link href="https://fonts.googleapis.com/css?family=Inconsolata" rel="stylesheet">
<style>
    * {
        font-family: 'Inconsolata', monospace;
        color: rgb(0, 0, 0);
    }
    body {
        background: linear-gradient(to right, rgb(24, 184, 168), rgb(118, 190, 50));;
    }
    .container {
        width: 320px;
        background: linear-gradient(to right, rgb(173, 58, 173), rgb(184, 63, 26));;
        margin: 120px auto;
    }
    table {
        width: 100%;
        border-color: #09646407;
        background: linear-gradient(to right, rgb(184, 24, 37), rgb(78, 13, 230));;
    }
    td {
        width: 25%;
        border-color: rgba(0, 0, 0, 0.363);
    }
    button {
        width: 100%;
        height: 70px;
        font-size: 24px;
        background: linear-gradient(to right, rgb(151, 11, 151), rgb(190, 94, 50));;      
        border: none;
    }
    #inputLabel {
        height: 120px;
        font-size: 40px;
        vertical-align: bottom;
        text-align: right;
        padding-right: 16px;
        background: linear-gradient(to right, rgb(4, 65, 88), rgb(226, 68, 47));;
    }
</style>
</head>
<body>
<div class="container">
    <table border="1" cellspacing="0">
        <tr>
            <td colspan="4" id="inputLabel">0</td>
        </tr>
        <tr>
            <td colspan="3"><button onclick="pushBtn(this);">AC</button></td>
            <td><button onclick="pushBtn(this);">/</button></td>
        </tr>
        <tr>
            <td><button onclick="pushBtn(this);">7</button></td>
            <td><button onclick="pushBtn(this);">8</button></td>
            <td><button onclick="pushBtn(this);">9</button></td>
            <td><button onclick="pushBtn(this);">*</button></td>
        </tr>
        <tr>
            <td><button onclick="pushBtn(this);">4</button></td>
            <td><button onclick="pushBtn(this);">5</button></td>
            <td><button onclick="pushBtn(this);">6</button></td>
            <td><button onclick="pushBtn(this);">-</button></td>
        </tr>
        <tr>
            <td><button onclick="pushBtn(this);">1</button></td>
            <td><button onclick="pushBtn(this);">2</button></td>
            <td><button onclick="pushBtn(this);">3</button></td>
            <td><button onclick="pushBtn(this);">+</button></td>
        </tr>
        <tr>
            <td colspan="2"><button onclick="pushBtn(this);">0</button></td>
            <td><button onclick="pushBtn(this);">.</button></td>
            <td><button onclick="pushBtn(this);">=</button></td>
        </tr>
    </table>
</div>
 
<script>
    var inputLabel = document.getElementById('inputLabel');
     
    function pushBtn(obj) {
         
        var pushed = obj.innerHTML;
         
        if (pushed == '=') {
            // Calculate
            inputLabel.innerHTML = eval(inputLabel.innerHTML);
             
        } else if (pushed == 'AC') {
            // All Clear
            inputLabel.innerHTML = '0';
             
        } else {
            if (inputLabel.innerHTML == '0') {
                inputLabel.innerHTML = pushed;
                 
            } else {
                inputLabel.innerHTML += pushed;   
            }
        }
    }
</script>
</body>
</html>

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