var zc=2*3.1415926*r
var mj=3.1415926*r*r
console.log('圆的周长为:'+zc)
console.log('圆的面积为:'+mj)
}
circle(2)
输入半径r即可输出对应周长和面积
1、JS画圆<script type="text/javascript">
//功能：画实心圆
//参数：圆心坐标，半径，精确度，背景颜色
//主要用到了中学时的圆的一些特征公式呵呵
function SolidCircle(centreX, centreY, radius, precision, color){
var cx = Math.abs(parseInt(centreX))
var cy = Math.abs(parseInt(centreY))
var r = parseInt(radius<2 ? 60 : radius)
var p = parseInt(precision<1 ? 1 : precision)
var c = color
var y
for(var x=cx-rx<=cx+rx+=p){
y = cy - Math.sqrt(Math.pow(r, 2) - Math.pow(cx - x, 2))
document.write('<img style="background:'+c+'border:1 solid '+c+'width:'+p+'height:'+parseInt(2*Math.sqrt(Math.pow(r, 2) - Math.pow(cx - x, 2)))+'position:absolutetop:'+parseInt(y)+'left:'+parseInt(x)+'">')
}
//alert("一共有 " + document.all.length + " 个 <img>")
}
SolidCircle(450, 100, 100, 1, "green")
</script>
2、计算器的连加原理其实和连续计算的原理是一样的，所以，在JS里面一定要定义一个全局变量，不论是加减乘除都调用这个变量即可。下面是一段完整的计算器代码，你可以参考一下，也可以解决你的问题。
<FORM name="Keypad" action="">
<TABLE>
<B>
<TABLE border=2 width=50 height=60 cellpadding=1 cellspacing=5>
<TR>
<TD colspan=3 align=middle>
<input name="ReadOut" type="Text" size=24 value="0" width=100%>
</TD>
<TD
</TD>
<TD>
<input name="btnClear" type="Button" value=" C " onclick="Clear()">
</TD>
<TD><input name="btnClearEntry" type="Button" value=" CE " onclick="ClearEntry()">
</TD>
</TR>
<TR>
<TD>
<input name="btnSeven" type="Button" value=" 7 " onclick="NumPressed(7)">
</TD>
<TD>
<input name="btnEight" type="Button" value=" 8 " onclick="NumPressed(8)">
</TD>
<TD>
<input name="btnNine" type="Button" value=" 9 " onclick="NumPressed(9)">
</TD>
<TD>
</TD>
<TD>
<input name="btnNeg" type="Button" value=" +/- " onclick="Neg()">
</TD>
<TD>
<input name="btnPercent" type="Button" value=" % " onclick="Percent()">
</TD>
</TR>
<TR>
<TD>
<input name="btnFour" type="Button" value=" 4 " onclick="NumPressed(4)">
</TD>
<TD>
<input name="btnFive" type="Button" value=" 5 " onclick="NumPressed(5)">
</TD>
<TD>
<input name="btnSix" type="Button" value=" 6 " onclick="NumPressed(6)">
</TD>
<TD>
</TD>
<TD align=middle><input name="btnPlus" type="Button" value=" + " onclick="Operation('+')">
</TD>
<TD align=middle><input name="btnMinus" type="Button" value=" - " onclick="Operation('-')">
</TD>
</TR>
<TR>
<TD>
<input name="btnOne" type="Button" value=" 1 " onclick="NumPressed(1)">
</TD>
<TD>
<input name="btnTwo" type="Button" value=" 2 " onclick="NumPressed(2)">
</TD>
<TD>
<input name="btnThree" type="Button" value=" 3 " onclick="NumPressed(3)">
</TD>
<TD>
</TD>
<TD align=middle><input name="btnMultiply" type="Button" value=" * " onclick="Operation('*')">
</TD>
<TD align=middle><input name="btnDivide" type="Button" value=" / " onclick="Operation('/')">
</TD>
</TR>
<TR>
<TD>
<input name="btnZero" type="Button" value=" 0 " onclick="NumPressed(0)">
</TD>
<TD>
<input name="btnDecimal" type="Button" value=" . " onclick="Decimal()">
</TD>
<TD colspan=3>
</TD>
<TD>
<input name="btnEquals" type="Button" value=" = " onclick="Operation('=')">
</TD>
</TR>
</TABLE>
</TABLE>
</B>
</FORM>
</CENTER>
<font face="Verdana, Arial, Helvetica" size=2>
<SCRIPT LANGUAGE="JavaScript">
<!-- Begin
var FKeyPad = document.Keypad
var Accum = 0
var FlagNewNum = false
var PendingOp = ""
function NumPressed (Num) {
if (FlagNewNum) {
FKeyPad.ReadOut.value = Num
FlagNewNum = false
}
else {
if (FKeyPad.ReadOut.value == "0")
FKeyPad.ReadOut.value = Num
else
FKeyPad.ReadOut.value += Num
}
}
function Operation (Op) {
var Readout = FKeyPad.ReadOut.value
if (FlagNewNum &&PendingOp != "=")
else
{
FlagNewNum = true
if ( '+' == PendingOp )
Accum += parseFloat(Readout)
else if ( '-' == PendingOp )
Accum -= parseFloat(Readout)
else if ( '/' == PendingOp )
Accum /= parseFloat(Readout)
else if ( '*' == PendingOp )
Accum *= parseFloat(Readout)
else
Accum = parseFloat(Readout)
FKeyPad.ReadOut.value = Accum
PendingOp = Op
}
}
function Decimal () {
var curReadOut = FKeyPad.ReadOut.value
if (FlagNewNum) {
curReadOut = "0."
FlagNewNum = false
}
else
{
if (curReadOut.indexOf(".") == -1)
curReadOut += "."
}
FKeyPad.ReadOut.value = curReadOut
}
function ClearEntry () {
FKeyPad.ReadOut.value = "0"
FlagNewNum = true
}
function Clear () {
Accum = 0
PendingOp = ""
ClearEntry()
}
function Neg () {
FKeyPad.ReadOut.value = parseFloat(FKeyPad.ReadOut.value) * -1
}
function Percent () {
FKeyPad.ReadOut.value = (parseFloat(FKeyPad.ReadOut.value) / 100) * parseFloat(Accum)
}
// End -->
</SCRIPT>
补充哦，怕在百度hi上给你的留言你看不到呵呵
----------------------------------------
那个圆也是没有问题的，因为给学生上课讲过这个算法，它有些类似于微积分中圆的面积求法，其实是将圆沿X轴进行细分，细分的精度由precision决定，所以，当你在这段代码中将精确降低的话，圆的边界就很粗糙，把细分后的每一块把它看成一个图形，这样累加起来，不就组成一个实习圆了嘛（截止到这儿，讲的是算法问题）。然后呢，代码的精髓在于那个For循环，(var x=cx-rx<=cx+rx+=p)表示变量是从圆的最左边开始的[因为圆心cx-半径r得到最左边，下同]，到最右边结束[cx+r]，而每次增加多少呢，是由精度控制的[x+=p]，然后循环体内的代码的精髓是图片的宽度和高度那块儿，宽度当然就等于精度了，高度的那个公式y = sqrt(r^2 - x^2)是画圆的必备公式，你应该明白吧。好了，到此为止，这段代码的原理和实现我都说到这儿了，希望你能明白。
