homework/calc.html at master · automotoby/homework · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Calculator</title>
    <style>
    #number1, #number2, #result2{
        width: 200px;
        height: 50px;
        font-size: 25px;
        display: inline-block;
        vertical-align: middle;
    }
    #but, #operation, #help{
        width: 100px;
        height: 50px;
        display: inline-block;
        vertical-align: middle;
        margin: 0 10px;
    }

    </style>
</head>
<body>
    <input id="number1">
    <select name="" id="operation" required>
        <option value="0">+</option>
        <option value="1">-</option>
        <option value="2">*</option>
        <option value="3">/</option>
        <option value="4">%</option>
    </select>
    <input id="number2">
    <input id="but" type="button" onclick="javascript:calculate();" value="=">
    <input id="help" type="button" onclick="javascript:help();" value="help">
    <div id="result2"> </div>


<script>
     var opArray = ['+','-','*','/','%'];
     function help(){
         var help = '';
         var counter = 0;
         while (counter < opArray.length){
             help+= opArray[counter] + ' моя функция \n\n';
             counter++;

         }
         alert(help)
     }
     function calculate(){
         var el1 = document.getElementById("number1"),
			 el2 = document.getElementById("number2"),
			 op = document.getElementById("operation");
         if (el1 && el2 && op){
            var left = parseInt(el1.value),
				right = parseInt(el2.value),
				operator = op.value;
            if (!isNaN(left) && !isNaN(right)){

                switch (opArray[+operator]){
                    case "+": setResult(left + right);
                    break;
                    case "-": setResult(left - right);
                    break;
                    case "*": setResult(left * right);
                    break;
                    case "/": setResult(left / right);
                    break;
                    case "%": setResult(left % right);
                    break;
                    default: alert("Wrong operation");
                }

            } else{
                alert("Error");
            }
         } else {
             alert("no element");
         }
     }
     function setResult(res) {
      document.getElementById("result2").innerHTML = "<b>Result is</b>: " + res;
    }
</script>
</body>
</html>