/*
Script by: Peter Bonnett
Script © Peter Bonnett 2001 
Web Site:  http://www.pete-b.co.uk
*/
document.calculator = document.getElementById("calculator");
function addition(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input two numbers')
}
else if (calculator.y.value.length == 0) {
alert('Please input two numbers')
}
else if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else if (isNaN(calculator.y.value)) {
alert('Please input only numbers!')
}
else {
x=eval(calculator.x.value)
y=eval(calculator.y.value)
c=x+y
alert(calculator.x.value + ' + ' + calculator.y.value +' = ' + c)
}
}

function subtraction(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input two numbers')
}
else if (calculator.y.value.length == 0) {
alert('Please input two numbers')
}
else if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else if (isNaN(calculator.y.value)) {
alert('Please input only numbers!')
}
else {
x=eval(calculator.x.value)
y=eval(calculator.y.value)
c=x-y
alert(calculator.x.value + ' - ' + calculator.y.value +' = ' + c)
}
}

function multiplication(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input two numbers')
}
else if (calculator.y.value.length == 0) {
alert('Please input two numbers')
}
else if (isNaN(calculator.y.value)) {
alert('Please input only numbers!')
}
else if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
x=eval(calculator.x.value)
y=eval(calculator.y.value)
c=x*y
alert(calculator.x.value + ' x ' + calculator.y.value +' = ' + c)
}
}

function division(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input two numbers')
}
else if (calculator.y.value.length == 0) {
alert('Please input two numbers')
}
else if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else if (isNaN(calculator.y.value)) {
alert('Please input only numbers!')
}
else {
x=eval(calculator.x.value)
y=eval(calculator.y.value)
c=x/y
alert(calculator.x.value + ' ÷ ' + calculator.y.value +' = ' + c)
}
}

function cmtoinch(calculator) {
if (calculator.x.value == 1) {
x=eval(calculator.x.value)
c=x/2.54
alert(x +' centimetre is ' + c + ' inches ')
}
else {
cm_inch(calculator);
}
}

function cm_inch(calculator) {
if (calculator.x.value == 2.54) {
x=eval(calculator.x.value)
c=x/2.54
alert(x +' centimetres is ' + c + ' inch ')
}
else {
cm_inch2(calculator);
}
}

function cm_inch2(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
cm_inch3(calculator);
}
}
function cm_inch3(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
cm_inch4(calculator)
}
}

function cm_inch4(calculator) {
if (calculator.x.value <= 0) {
alert('Please input a number higher than 0!')
}
else {
cm_inch5(calculator)
}
}

function cm_inch5(calculator) {
x=eval(calculator.x.value)
c=x/2.54
alert(x +' centimetres are ' + c + ' inches')
}

function inchtocm(calculator) {
if (calculator.x.value == 1) {
x=eval(calculator.x.value)
c=x*2.54
alert(x +' inch is ' + c + ' centimetres ')
}
else {
inch_cm(calculator);
}
}

function inch_cm(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
inch_cm2(calculator);
}
}

function inch_cm2(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
inch_cm3(calculator)
}
}

function inch_cm3(calculator) {
if (calculator.x.value <= 0) {
alert('Please input a number higher than 0!')
}
else {
inch_cm4(calculator)
}
}

function inch_cm4(calculator) {
x=eval(calculator.x.value)
c=x*2.54
alert(x +' inches are ' + c + ' centimetres ')
}

function mtokm(calculator) {
if (calculator.x.value == 1) {
x=eval(calculator.x.value)
c=x/1.609344
alert(x +' mile is ' + c + ' kilometres')
}
else {
m_km(calculator);
}
}

function m_km(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
m_km2(calculator);
}
}

function m_km2(calculator) {
if (calculator.x.value == 1.609344) {
x=eval(calculator.x.value)
c=x/1.609344
alert(x +' miles are ' + c + ' kilometre ')
}
else {
m_km3(calculator);
}
}

function m_km3(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
m_km4(calculator)
}
}

function m_km4(calculator) {
if (calculator.x.value <= 0) {
alert('Please input a number higher than 0!')
}
else {
m_km5(calculator)
}
}

function m_km5(calculator) {
x=eval(calculator.x.value)
c=x/1.609344
alert(x +' miles are ' + c + ' kilometres ')
}

function kmtom(calculator) {
if (calculator.x.value == 1) {
x=eval(calculator.x.value)
c=x*1.609344
alert(x +' kilometre is ' + c + ' miles ')
}
else {
km_m(calculator);
}
}

function km_m(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
km_m2(calculator);
}
}

function km_m2(calculator) {
if (calculator.x.value <= 0) {
alert('Please input a number higher than 0!')
}
else {
km_m3(calculator)
}
}

function km_m3(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
km_m4(calculator)
}
}

function km_m4(calculator) {
x=eval(calculator.x.value)
c=x*1.609344
alert(x +' kilometres  ' + c + ' miles ')
}

function degree_ctof(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
ctof(calculator);
}
}

function ctof(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
ctof2(calculator)
}
}

function ctof2(calculator){
x=eval(calculator.x.value)
c=x*1.8+32
alert(x +' ° C is ' + c + ' ° F')
}

function degree_ftoc(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
ftoc(calculator);
}
}

function ftoc(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
ftoc2(calculator)
}
}

function ftoc2(calculator) {
x=eval(calculator.x.value)
c=(x-32)*5/9
alert(x +' ° F is ' + c + ' ° C')
}

function degree_ctok(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
ctok(calculator);
}
}

function ctok(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
ctok2(calculator)
}
}

function ctok2(calculator) {
x=eval(calculator.x.value)
c=x+273.15
alert(x +' ° C is ' + c + ' K')
}

function degree_ktoc(calculator) {
if (calculator.x.value <0) {
alert('Please enter a positive number!');}
else {
ktoc(calculator);
}
}

function ktoc(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
ktoc2(calculator);
}
}

function ktoc2(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
ktoc3(calculator)
}
}

function ktoc3(calculator) {
x=eval(calculator.x.value)
c=x-273.15
alert(x +' K is ' + c + ' ° C')
}

function degree_ktof(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
ktof(calculator);
}
}

function ktof(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
ktof2(calculator)
}
}

function ktof2(calculator) {
if (calculator.x.value <0) {
alert('Please enter a positive number!');}
else {
ktof3(calculator);
}
}

function ktof3(calculator) {
x=eval(calculator.x.value)
c=(x-273.15)*1.8+32
alert(x +' K is ' + c + ' ° F')
}

function degree_ftok(calculator) {
if (calculator.x.value.length == 0) {
alert('Please input a number')
}
else {
ftok(calculator);
}
}

function ftok(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
ftok2(calculator)
}
}

function ftok2(calculator) {
x=eval(calculator.x.value)
c=((x-32)*5/9)+273.15
alert(x +' ° F is ' + c + ' K')
}


function mptokp(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
mp_kp(calculator)
}
}

function mp_kp(calculator) {
if (calculator.x.value <= 0) {
alert('Please input a number higher than 0!')
}
else {
mp_kp2(calculator)
}
}

function mp_kp2(calculator) {
x=eval(calculator.x.value)
c=x/1.609344
alert(x +' mph is ' + c + ' kph ')
}

function kptomp(calculator) {
if (isNaN(calculator.x.value)) {
alert('Please input only numbers!')
}
else {
kp_mp(calculator)
}
}

function kp_mp(calculator) {
if (calculator.x.value <= 0) {
alert('Please input a number higher than 0!')
}
else {
mp_kp2(calculator)
}
}

function kp_mp2(calculator) {
x=eval(calculator.x.value)
c=x*1.609344
alert(x +' kph is ' + c + ' mph ')
}