<input type=text id="c" onchange="doit()">
function doit()
{
document.all["d"].value=document.all["a"].value*document.all["b"].value+document.all["c"].value
}
function doit()
{
document.all["d"].value=document.all["a"].value*document.all["b"].value+document.all["c"].value
}
<input type=text name=a value="">
<input type=text name=b value="">
<input type=text name=c value="">
<input type=text name=d value="">
<input type=button value="count" onclick=fuckmm>
</form>
<script>
function fuckmm(){
var one=eval(document.form1.a.value)
var two=eval(document.form1.b.value)
var three=eval(docuemnt.form1.c.value)
total=one*two+three
document.form1.d.value=total
}
</script>
a:
<input name="a" type="text" onpropertychange="change_value();"><br>
b:
<input name="b" type="text" onpropertychange="change_value();"><br>
c:
<input name="c" type="text" onpropertychange="change_value();"><br>
d:
<input name="d" type="text" readonly>
<script>
<!--
function change_value() {
var aa=document.all.a.value;
var bb=document.all.b.value;
var cc=document.all.c.value;
if(aa==""||bb==""||cc=="")
return;
try {
document.all.d.value=parseInt(aa)*parseInt(bb)+parseInt(cc);
} catch(e) {}
}
//-->
</script>
******************
公式:d=a*b+c<br>
a:
<input name="a" type="text" onpropertychange="change_value();"><br>
b:
<input name="b" type="text" onpropertychange="change_value();"><br>
c:
<input name="c" type="text" onpropertychange="change_value();"><br>
d:
<input name="d" type="text" readonly>
<script>
<!--
function change_value() {
var aa=document.all.a.value;
var bb=document.all.b.value;
var cc=document.all.c.value;
if(aa==""||bb==""||cc=="") {
document.all.d.value="";
return;
}
try {
document.all.d.value=parseInt(aa)*parseInt(bb)+parseInt(cc);
} catch(e) {
document.all.d.value="";
}
}
//-->
</script>
B: <input type=text name=t2><br>
C: <input type=text name=t3><br>
D: <input type=text name=t4 readonly><br>
<input type=button value=计算 onclick="cc()"><script language=javascript>
function cc()
{
var a = document.all.t1.value;
var b = document.all.t2.value;
var c = document.all.t3.value;
if (a=="" || b=="" || c==""){alert("不能为空");return;}
if (!(a.match(/\D/)==null) || !(b.match(/\D/)==null) || !(c.match(/\D/)==null))
{alert("你输入的不是整数或数字!");return;}
a = parseFloat(a);
b = parseFloat(b);
c = parseFloat(c);
var d = a * b + c;
document.all.t4.value = d;
}
</script>