入门-2

优先使用//注释

二元运算符前后各加一个空格，提高程序的可读性

javascript会自动进行类型的转换

ch4_6.html

<!DOCTYPE html>
<html>
<head>
    <title>Pringting Multiple Lines</title>
    <script type="text/javascript">
        <!--
        var firstNumber;
        var secondNumber;
        var num1;
        var num2;
        var sum;

        firstNumber = window.prompt("Enter the first number:");
        num1 = parseInt(firstNumber);

        secondNumber = window.prompt("Enter the second number:");
        num2 = parseInt(secondNumber);

        sum = num1 + num2;

        document.writeln("<h1>The sum is " + sum + "</h1>")


        //-->
    </script>
</head>
<body>
<p>please refresh or reload this script again!</p>
</body>
</html>

ch4_7.html

<!DOCTYPE html>
<html>
<head>
    <title>Pringting Multiple Lines</title>
    <script type="text/javascript">
        <!--
        var name;
        var now = new Date();
        var hour = now.getHours();

        name = window.prompt("Enter your name:");

        if(hour<12)
            document.write("<h1>Good morning!");

        if(hour >=12)
        {
            hour = hour - 12;

            if( hour > 6 )
                document.write("<h1>Good afternoon!");
            else
                document.write("<h1>Good evening!");
        }

        document.writeln( name + ", welcome to javascript programming!</h1>");
        //-->
    </script>
</head>
<body>
<p>please refresh or reload this script again!</p>
</body>
</html>

www.deitel.com/javascript Deitel公司的javascript资源中心

ch4_8.html

<!DOCTYPE html>
<html>
<head>
    <title>Pringting Multiple Lines</title>
    <script type="text/javascript">
        <!--
        var total;
        var gradeCounter;
        var grade;
        var gradeValue;
        var average;

        total = 0;

        gradeCounter = 1;

        while( gradeCounter <= 10 )
        {
            grade = window.prompt("Enter the grade:");

            gradeValue = parseInt( grade );

            total = total + gradeValue;

            gradeCounter = gradeCounter + 1;
        }

        average = total / 10;

        document.writeln("<h1>Class average is " + average + "</h1>");
        //-->
    </script>
</head>
<body>
<p>please refresh or reload this script again!</p>
</body>
</html>

ch4_9.html

<!DOCTYPE html>
<html>
<head>
    <title>Pringting Multiple Lines</title>
    <script type="text/javascript">
        <!--
        var total;
        var gradeCounter;
        var grade;
        var gradeValue;
        var average;

        total = 0;

        gradeCounter = 0;

        grade = window.prompt("Enter the grade:(-1 to quit)","0");
        gradeValue = parseInt( grade );

        while( gradeValue != -1 )
        {
            grade = window.prompt("Enter the grade:(-1 to quit)","0");

            gradeValue = parseInt( grade );

            total = total + gradeValue;

            gradeCounter = gradeCounter + 1;
        }

        if( gradeCounter != 0 )
        {
            average = total / gradeCounter;

            document.writeln("<h1>Class average is " + average + "</h1>");
        }
        else
            document.writeln("<p>No grades were entered.</p>");
        //-->
    </script>
</head>
<body>
<p>please refresh or reload this script again!</p>
</body>
</html>

ch4_10.html

<!DOCTYPE html>
<html>
<head>
    <title>Pringting Multiple Lines</title>
    <script type="text/javascript">
        <!--
        var passes = 0;
        var failures = 0;
        var student = 1;
        var result;

        while( student <= 10 )
        {
            result = window.prompt("Enter result(1=pass,0=fail)","0");

            if( result == "1" )
                passes = passes + 1;
            else
                failures = failures + 1;

            student = student + 1;
        }

        document.writeln("<h1>Examination results:</h1>");
        document.writeln("Pass: " + passes + "</br>Fail: " + failures );

        if( passes > 8 )
        document.writeln("</br>Raised Tuition");


        //-->
    </script>
</head>
<body>
<p>please refresh or reload this script again!</p>
</body>
</html>

ch4_11.html

<!DOCTYPE html>
<html>
<head>
    <title>Pringting Multiple Lines</title>
    <script type="text/javascript">
        <!--
        var c;

        c = 5;

        document.writeln("<h3>Postcrement Demo</h3>");
        document.writeln(c);
        document.writeln( "</br>" + (c++) );
        document.writeln( "</br>" +  c );

        c = 5;

        document.writeln("<h3>precrement Demo</h3>");
        document.writeln(c);
        document.writeln( "</br>" + (++c) );
        document.writeln(  "</br>" + c );
        //-->
    </script>
</head>
<body>
<p>please refresh or reload this script again!</p>
</body>
</html>