JavaScript/addition-program-with-validation.html at master · eliCoding/JavaScript · GitHub

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<!DOCTYPE html>

<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="utf-8" />
    <title></title>
    <script type="text/javascript">
        /*prompt the user to enter 2 numbers and then display te sum*/

        //1.Declaration Phase
        var firstNumber; // first number entered by user  as a string
        var secondNumber;  //second number entered bu used as a  strng
        var number1;   //converted first number
        var number2; //converted second number
        var sum;   //sum of number 1 and number 2
        // 2. Initialization Phase
        //read first number from a user as a String

        //ensure that the value is numerical
        while (isNaN(firstNumber = window.prompt("Please Enter First Number", "0"))) {
            window.prompt("You have enterted" + firstNumber + ".Please enter a number");

        } //end while loop
        while (isNaN(secondNumber = window.prompt("Please Enter Second Number", "0"))) {
            window.prompt("You have enterted" + secondNumber + ".Please enter a number");

        } //end while loop
        sum = 0;

        //3. Processing Phase
        firstNumber = window.prompt("Enter first number");
        number1 = parseFloat(firstNumber);
        secondNumber = window.prompt("Enter second number");
        number2 = parseFloat(secondNumber);
        //add number one and number 2 to sum
        sum = number1+number2;


        //4. Termination Phase
        document.writeln("<h2> the sum of "+firstNumber+" + "+secondNumber+ " + " +sum.toPrecision(2) + "</h2>");


    </script>
</head>
<body>

</body>
</html>