My "math" library from when I first started coding.

math.js

function doMath()
{
    var mathCond = document.getElementById("mcond").value;
    if ((mathCond == "x") || (mathCond == "*") || (mathCond == "times") || (mathCond == "multiply"))
        var output = multiplyMath();
    else if ((mathCond == "+") || (mathCond == "add") || (mathCond == "plus"))
        var output = addMath();
    else if ((mathCond == "-") || (mathCond == "subtract") || (mathCond == "minus"))
        var output = subtractMath();
    else if ((mathCond == "/") || (mathCond == "divide"))
        var output = divideMath();
    else if ((mathCond == "rtc") || (mathCond == "radiustocircumference"))
        var output = rtocMath();
    else if ((mathCond == "dtc") || (mathCond == "diametertocircumference"))
        var output = dtocMath();
    else if ((mathCond == "sqrt") || (mathCond == "square root"))
        var output = sqrtMath();
    else if ((mathCond == "^") || (mathCond == "power") || (mathCond == "pwr") || (mathCond == "pow"))
        var output = pwrMath();
    else if ((mathCond == "dectodeg") || (mathCond == "decimaltodegree"))
        var output = dectodegMath();
    else if ((mathCond == "degtodec") || (mathCond == "degreetodecimal"))
        var output = degtodecMath();
    else if ((mathCond == "sine") || (mathCond == "sin"))
        var output = sinMath();
    else if ((mathCond == "cosine") || (mathCond == "cos"))
        var output = cosMath();
    else if ((mathCond == "tangent") || (mathCond == "tan"))
        var output = tanMath();
    else if ((mathCond == "coin") || (mathCond == "coin flip"))
        var output = coinRand();
    else if ((mathCond == "floatrand") || (mathCond == "floating point") || (mathCond == "0-1"))
        var output = floatRand();
    else if ((mathCond == "percent") || (mathCond == "out of 100") || (mathCond == "%"))
        var output = percentRand();
    else if ((mathCond == "integer") || (mathCond == "random integer") || (mathCond == "randint"))
        var output = intRand();
    else
        alert("The operator you have chosen is not valid. All valid operators are inside the drop-down menu.");
    var mout = document.getElementById("mout");
    mout.innerHTML = "The result is: <br> <input type='text' class='mainf' value='" + output + "' id='mcondbox'>";
}
function multiplyMath()
{
    var input1 = document.getElementById("minput1").value;
    var input2 = document.getElementById("minput2").value;
    var input3 = document.getElementById("minput3").value;
    var input4 = document.getElementById("minput4").value;
    var input5 = document.getElementById("minput5").value;
    if (input2 == "")
        input2 = 1;
    if (input3 == "")
        input3 = 1;
    if (input4 == "")
        input4 = 1;
    if (input5 == "")
        input5 = 1;
    var output = input1 * input2 * input3 * input4 * input5;
    return output;
}
function addMath() {
    var input1 = Number(document.getElementById("minput1").value);
    var input2 = Number(document.getElementById("minput2").value);
    var input3 = Number(document.getElementById("minput3").value);
    var input4 = Number(document.getElementById("minput4").value);
    var input5 = Number(document.getElementById("minput5").value);
    if (input2 == "")
        input2 = 0;
    if (input3 == "")
        input3 = 0;
    if (input4 == "")
        input4 = 0;
    if (input5 == "")
        input5 = 0;
    var output = input1 + input2 + input3 + input4 + input5;
    return output;
}
function divideMath() {
    var input1 = document.getElementById("minput1").value;
    var input2 = document.getElementById("minput2").value;
    var input3 = document.getElementById("minput3").value;
    var input4 = document.getElementById("minput4").value;
    var input5 = document.getElementById("minput5").value;
    if (input2 == "")
        input2 = 1;
    if (input3 == "")
        input3 = 1;
    if (input4 == "")
        input4 = 1;
    if (input5 == "")
        input5 = 1;
    var output = input1 / input2 / input3 / input4 / input5;
    if (output == "Infinity") {
        alert("You divided by zero, didn't you? Don't worry, it won't break.");
        output = "Infinity!!!!";
    }
    return output;
}
function subtractMath() {
    var input1 = document.getElementById("minput1").value;
    var input2 = document.getElementById("minput2").value;
    var input3 = document.getElementById("minput3").value;
    var input4 = document.getElementById("minput4").value;
    var input5 = document.getElementById("minput5").value;
    if (input2 == "")
        input2 = 0;
    if (input3 == "")
        input3 = 0;
    if (input4 == "")
        input4 = 0;
    if (input5 == "")
        input5 = 0;
    var output = input1 - input2 - input3 - input4 - input5;
    return output;
}
function clearMath()
{
    document.getElementById("minput1").value = "";
    document.getElementById("minput2").value = "";
    document.getElementById("minput3").value = "";
    document.getElementById("minput4").value = "";
    document.getElementById("minput5").value = "";
    document.getElementById("mcondbox").value = "";
}
function rtocMath()
{
    var value1 = document.getElementById("minput1").value;
    var output = Math.PI * value1 * value1;
    return output;
}
function dtocMath()
{
    var value1 = document.getElementById("minput1").value;
    var output = Math.PI * value1;
    return output;
}
function sqrtMath()
{
    var value1 = document.getElementById("minput1").value;
    var output = Math.sqrt(value1);
    return output;
}
function pwrMath()
{
    var value1 = document.getElementById("minput1").value;
    var value2 = document.getElementById("minput2").value;
    var output = Math.pow(value1, value2);
    return output;
}
function dectodegMath()
{
    var value1 = document.getElementById("minput1").value;
    var output = value1 * 360;
    return output;
}
function degtodecMath() {
    var value1 = document.getElementById("minput1").value;
    var output = value1 / 360;
    return output;
}
function cosMath() {
    var value1 = document.getElementById("minput1").value;
    var output = Math.cos(value1);
    return output;
}
function sinMath() {
    var value1 = document.getElementById("minput1").value;
    var output = Math.sin(value1);
    return output;
}
function tanMath() {
    var value1 = document.getElementById("minput1").value;
    var output = Math.tan(value1);
    return output;
}
function coinRand() {
    var rand = Math.random();
    if (rand <= 0.50)
        var output = "Tails";
    else
        var output = "Heads";
    return output;
}
function floatRand() {
    return Math.random();
}
function percentRand() {
    var rand = Math.random() * 100;
    var output = Math.round(rand) + "%";
    return output;
}
function intRand() {
    var value1 = document.getElementById("minput1").value;
    var value2 = document.getElementById("minput2").value;
    var randroot = Math.random();
    if (value2 == "max")
    {
        var length = value1.toString().length;
        if (length > 16) {
            alert("The number of digits is too high. Enter a number smaller than 17 digits long.");
            return "Try again!!";
        }
        var mul = 1;
        for (i = 0; i < length; i++)
            var mul = mul * 10;
        var result = randroot * mul
        var parsed = parseInt(result)
        while ((parsed > value1) || (parsed == 0)) {
            randroot = Math.random();
            result = randroot * mul;
            parsed = parseInt(result);
        }
        var psl = parsed.toString().length;
        while (psl < length) {
            parsed = "0" + parsed;
            psl = parsed.length;
        }
        return parsed;
    }
    else if ((value2 == "digits") || (value2 == "")) {
        var length = value1.toString();
        if (length > 16) {
            alert("The number of digits is too high. Enter a number smaller than 17.");
            return "Try again!!";
        }
        var mul = 1;
        for (i = 0; i < length; i++)
            var mul = mul * 10;
        var result = randroot * mul;
        var parsed = parseInt(result);
        var psl = parsed.toString().length;
        while (psl < length) {
            parsed = "0" + parsed;
            psl = parsed.length;
        }
        return parsed;
    }
    else {
        alert("There was an invalid argument in the second box. Try either 'max' or 'digits'.");
        return "Try again!!";
    }
}
$(document).ready(function () {
    var cond = document.getElementById("mcond");
    $("#mcondsel").click(function () {
        $("#mcondmenu").slideToggle("fast");
    });
    $("#addmathlist").click(function () {
        cond.value = "add";
    });
    $("#minmathlist").click(function () {
        cond.value = "subtract";
    });
    $("#mulmathlist").click(function () {
        cond.value = "multiply";
    });
    $("#divmathlist").click(function () {
        cond.value = "divide";
    });
    $("#sqrmathlist").click(function () {
        cond.value = "square root";
    });
    $("#pwrmathlist").click(function () {
        cond.value = "power";
    });
    $("#rtcmathlist").click(function () {
        cond.value = "rtc";
    });
    $("#dtcmathlist").click(function () {
        cond.value = "dtc";
    });
    $("#gtimathlist").click(function () {
        cond.value = "degtodec";
    });
    $("#itgmathlist").click(function () {
        cond.value = "dectodeg";
    });
    $("#cosmathlist").click(function () {
        cond.value = "cosine";
    });
    $("#sinmathlist").click(function () {
        cond.value = "sine";
    });
    $("#tanmathlist").click(function () {
        cond.value = "tangent";
    });
    $("#flimathlist").click(function () {
        cond.value = "coin flip";
        doMath();
    });
    $("#dcrmathlist").click(function () {
        cond.value = "floatrand";
        doMath();
    });
    $("#prcmathlist").click(function () {
        cond.value = "percent";
        doMath();
    });
    $("#intmathlist").click(function () {
        cond.value = "randint";
    });
    $("#minputtog").click(function () {
        $("#minputmore").slideToggle("fast");
    });
    $("#arthtog").click(function () {
        $("#arthlist").slideToggle("fast");
    });
    $("#spectog").click(function () {
        $("#speclist").slideToggle("fast");
    });
    $("#trigtog").click(function () {
        $("#triglist").slideToggle("fast");
    });
    $("#autotog").click(function () {
        $("#autolist").slideToggle("fast");
    });
    $("#randtog").click(function () {
        $("#randlist").slideToggle("fast");
    });
    $(".mathlist").click(function () {
        $("#mcondmenu").slideToggle("fast");
        $("#mcondsel").toggleClass("dtoggle utoggle");
        clearMath();
    });
});
$(function () {
    $(document).tooltip();
});

math2.js

// The half-finished array-based maths code. My favourite is findQuantArray().
function doArray() {
	var arrCond = document.getElementById("acond").value;
	if (arrCond = "mean")
		var out = meanArray();
	else if (arrCond = "median")
		var out = medianArray();
	else {
		alert("The operator you have chosen is invalid. Please try again.");
		var out = "Try again!!!";
	}
	var aout = document.getElementById("aout");
	aout.value = out;
	return out;
}
function getArray() {
	var vArray = [];
	var v0 = null; 
	var v1 = document.getElementById("a1").value;
	var v2 = document.getElementById("a2").value;
	var v3 = document.getElementById("a3").value;
	var v4 = document.getElementById("a4").value;
	var v5 = document.getElementById("a5").value;
	var v6 = document.getElementById("a6").value;
	var v7 = document.getElementById("a7").value;
	var v8 = document.getElementById("a8").value;
	var v9 = document.getElementById("a9").value;
	var v10 = document.getElementById("a10").value;
	var v11 = document.getElementById("a11").value;
	var v12 = document.getElementById("a12").value;
	var v13 = document.getElementById("a13").value;
	var v14 = document.getElementById("a14").value;
	var v15 = document.getElementById("a15").value;
	var v16 = document.getElementById("a16").value;
	var v17 = document.getElementById("a17").value;
	var v18 = document.getElementById("a18").value;
	var v19 = document.getElementById("a19").value;
	var v20 = document.getElementById("a20").value;
	vArray.push(v0, v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, 
	v14, v15, v16, v17, v18, v19, v20);
	return vArray;
}
function clearArray() {
	document.getElementById("a1").value = "";
	document.getElementById("a2").value = "";
	document.getElementById("a3").value = "";
	document.getElementById("a4").value = "";
	document.getElementById("a5").value = "";
	document.getElementById("a6").value = "";
	document.getElementById("a7").value = "";
	document.getElementById("a8").value = "";
	document.getElementById("a9").value = "";
	document.getElementById("a10").value = "";
	document.getElementById("a11").value = "";
	document.getElementById("a12").value = "";
	document.getElementById("a13").value = "";
	document.getElementById("a14").value = "";
	document.getElementById("a15").value = "";
	document.getElementById("a16").value = "";
	document.getElementById("a17").value = "";
	document.getElementById("a18").value = "";
	document.getElementById("a19").value = "";
	document.getElementById("a20").value = "";
}
function findQuantArray() {
	var ar = getArray();
	if (ar[20] !== "") // full input failsafe
		return 20;
	else {
		var n = ar[0];
		for (var i=1;n !== "";i++) { // checks to see first empty input
			var n = ar[i];
		}
		i = i - 2; // makes number correct
		return i;
	}
}
function meanArray() {
	var ar = getArray();
	var quant = findQuantArray();
/*	for (i=1;i < quant;i++) {
		if (i == 1)
			var result = addMath(ar[1],ar[2]);
		else {
			var o = i++;
			result = addMath(result,ar[o]);
		}
	}*/
	var result = 42;
	var out = result / quant;
	return out;
}
function addArray() {
	var ar = getArray();
	var qu = findQuantArray();
	var rs = qu/5;
}
function medianArray() {
	var quant = findQuantArray();
	return parseInt(quant / 2);
}