// JavaScript Document
/*
 *This JavaScript simulates the operation of a real calculator. The keys respond 
 *according to previous functions and type of entry. The memory function allows you
 *to store values for future use, and to add and subtract from the stored value. The
 *indicator windows shows an 'M' if there is a value stored in memory. There are also
 *a few special function keys and a stored constant.
 *
 *Copyright 1997, David Turley <dturley@pobox.com>
 *Feel free to use and build on this code as long as you include this notice.
 *Last Modified May 30, 1997
 *
 *Simplified and added CSS on freeonlinecalculator.net September 2, 2009 now www.calculatorsoup.com
*/

//flags to mark previous function
var opFlag=false 	//indicates previous entry was an operator
var eqFlag=false 	//indicates previous function was a calculation


function checkDec() {
//prevents multiple decimal points in entry
	if (document.calc.screen.value.indexOf('.') == -1){
		enterVal('.')
		return
	}

		if ((document.calc.screen.value.indexOf('.') >= 0) && ((eqFlag) || (opFlag))){
		enterVal('.')
		return
	}
	
}

function enterVal(num){		
//determine how to handle entry based on previous function

		
	if (eqFlag) {
	//last entry gave a total, no operators entered, so replace both stores
		document.calc.input.value=num
		document.calc.screen.value=num
		eqFlag=false
		return
	}
	
	if ((!opFlag) && (!eqFlag)){
	//no operators or totals entered, still entering numbers
		document.calc.input.value += num
		document.calc.screen.value += num
		return				
	}

	if (opFlag) {
	//operator entered, change screen value, build on input
		document.calc.screen.value =num
		document.calc.input.value += num
		opFlag=false
		return
	}	

}

function compute() {
//if last entry is an operator, input is not complete so do nothing

	len=document.calc.input.value.length
	var oneChar=document.calc.input.value.charAt(len-1)
	if ((oneChar == '+') || (oneChar == '-') || (oneChar == '*') ||
		(oneChar == '/')) {	
		return
	}

	document.calc.screen.value = eval(document.calc.input.value)
	document.calc.input.value = eval(document.calc.input.value)
	
	eqFlag=true
	
	
}

function operator(op) {
	//can't enter operator before entering a value
	if (document.calc.screen.value == ''){
		return
	}

	//if last entry is not an operator, use the one just entered
	eqFlag=false
	len=document.calc.input.value.length
	var oneChar=document.calc.input.value.charAt(len-1)
	if ((oneChar != '+') && (oneChar != '-') && (oneChar != '*') &&
		(oneChar != '/') && (oneChar != '.')){
			document.calc.screen.value = eval(document.calc.input.value)
			document.calc.input.value = eval(document.calc.input.value)
			document.calc.input.value += op
			
	}
	else { 		
	//if last entry is an operator, replace it with this one
	//this returns input store less operator
		document.calc.input.value=parseFloat(document.calc.input.value)
		document.calc.input.value+=op
	}
	opFlag=true
}

function clearAll() {
	document.calc.input.value = ''
	document.calc.screen.value=''
	
}

function clearEntry() {
	//don't do anything if the last entry is not a number
	len=document.calc.input.value.length
	var oneChar=document.calc.input.value.charAt(len-1)
	if ((oneChar == '+') || (oneChar == '-') || (oneChar == '*') ||
		(oneChar == '/')) {	
		return
	}
	
	if (document.calc.screen.value == ''){
	//nothing here to clear
		return
	}
	
	if (document.calc.screen.value==document.calc.input.value) {  
	//only one entry, so clear it
		document.calc.screen.value=''
		document.calc.input.value=''
		return
	}
		//get last number entered and clear it, return previous value to screen
		str1=document.calc.screen.value
		str2=document.calc.input.value
		ind=str2.lastIndexOf(str1)
		document.calc.input.value=document.calc.input.value.substring(0,ind)
		document.calc.screen.value=parseFloat(document.calc.input.value)
		
}
function sqrRT() {

	if (document.calc.input.value == ''){
	//nothing entered, do nothing
		return
	}

	document.calc.screen.value=Math.sqrt(document.calc.screen.value)
	document.calc.input.value=document.calc.screen.value
	eqFlag=true
}

function sqr() {

	if (document.calc.input.value == ''){
		return
	}
	
	document.calc.screen.value=(document.calc.screen.value)*(document.calc.screen.value)
	document.calc.input.value=document.calc.screen.value
	eqFlag=true
}

function neg() {//get last entry and negate it
	str1=document.calc.screen.value
	str2=document.calc.input.value
	ind=str2.lastIndexOf(str1)

	document.calc.input.value=document.calc.input.value.substring(0,ind)
	document.calc.screen.value=(document.calc.screen.value)*-1
	document.calc.input.value += "(" + document.calc.screen.value + ")"
	//placed in () to solve double operator problem
}
	

function pcnt() {

	if (document.calc.input.value == ''){ //nothing here
		return
	}
	//if last entry is an operator, do nothing
	len=document.calc.input.value.length  
	var oneChar=document.calc.input.value.charAt(len-1)
	if ((oneChar == '+') || (oneChar == '-') || (oneChar == '*') ||
		(oneChar == '/')) {	
		return
	}
	//check that there are two numbers entered
	if ((document.calc.input.value.indexOf('+') == -1)&& 
	(document.calc.input.value.indexOf('-') == -1)&&
	(document.calc.input.value.indexOf('*') == -1)&&
	(document.calc.input.value.indexOf('/') == -1)){
		return
	}
	//calculate percentage

	if ((document.calc.input.value.indexOf('+') != -1) || 
	(document.calc.input.value.indexOf('-') != -1)) {

		percent=((document.calc.screen.value)/100)*parseFloat(document.calc.input.value)
	
	}

	else {
		percent=((document.calc.screen.value)/100)
		
	}
	
	//replace last entry with percentage and evaluate expression
	str1=document.calc.screen.value
	str2=document.calc.input.value
	ind=str2.lastIndexOf(str1)

	document.calc.input.value=document.calc.input.value.substring(0,ind)
	document.calc.input.value+=percent
	document.calc.screen.value = eval(document.calc.input.value)
	document.calc.input.value = eval(document.calc.input.value)
	

	eqFlag=true
}

function memory_p() {
	if (document.calc.screen.value ==''){
		return
	}
	//add screen value to memory store
	document.calc.memory.value+= "+" + document.calc.screen.value
	document.calc.memory.value=eval(document.calc.memory.value)
	eqFlag=true
	document.calc.mem_win.value='M' //indicator of something in memory
	
}

function memory_s() {

	if (document.calc.screen.value ==''){
		return
	}

	document.calc.memory.value += "-(" + (document.calc.screen.value) +")"
	document.calc.memory.value=eval(document.calc.memory.value)

	eqFlag=1
	document.calc.mem_win.value='M' 

}

function memory_r() {
	//recall memory store to screen
	document.calc.screen.value=''
	enterVal(document.calc.memory.value)
	eqFlag=true
	
	
	
}

function memory_c() {
	//clear memory indicator
	document.calc.memory.value=0
	document.calc.mem_win.value=''  

}

function constant(what) {
	if (what == 'pi') {
		document.calc.screen.value=''
		enterVal(Math.PI)
		eqFlag=true
		
	}
}