Var and let simple beginner problem

B

bob116

Joined
Nov 8, 2019
Messages
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Hello, this is an elementary js problem,which is currently simplified until I get the below problem solved.
In function <b>select</b> I select 2 people at random.
In function <b>transfer</b>, there is a transfer of money from poorer to richer .
poorer and richer are calculated in function <b>select</b>
Problem is that richer and poorer are not recognised when control goes to function <b>transfer</b>.
I get "undefined" on line 45.
I know this is a simple matter of var and let, but I have not yet found a simple explanation of var and let and hoist on the web. Simple for a beginner like me, that is.
If I can get this sorted the rest will be easy.
Can anyone help?
Is there a reasonable site which explains var and let for a beginner?
And the significance of "use strict"?
I am retired and self-taught.
I was unable to copy/paste the .html from VSCode so here it is.


JavaScript: 
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>ginaCoeff</title>
</head>

<body>
    <script>
        var richer;
        var poorer;
        var N = 10;
        var startLevel = 100;
        var people = [];
        var trials = 100;
        var transferFrac = 0.20;

        function loadPeople(N) {
            for (let i = 0; i <= N - 1; i++) {
                people[i] = startLevel;
                console.log(i, people[i]);
            }
        }

        function select(N, richer, poorer) {
            var x = Math.floor(Math.random() * N) + 1;
            var y = Math.floor(Math.random() * N) + 1;
            if (x == y) {
                x = x + Math.floor(Math.random() * N) + 1;
                if (x > N) {
                    x = x - N;
                }
            }
            richer = Math.max(x, y);
            poorer = Math.min(x, y);
            console.log("fn select: " + "richer " + richer + "  poorer " + poorer);
        }

        function transfer(richer, poorer, transferFrac) {
            var richer;
            var poorer;
            console.log("fn transfer1: " + "richer " + richer + "  poorer " + poorer);
            var transferAmount = people[poorer] * transferFrac;
            people[richer] = people[richer] + transferAmount;
            people[poorer] = people[poorer] - transferAmount;
        }

        /////////////////////////////////////////////////////

        loadPeople(N);
        select(N, richer, poorer);
        transfer(richer, poorer, transferFrac);
        console.log(people[richer] + "   " + people[poorer]);


    </script>
</body>

</html>
 
sunfighter

sunfighter

Joined
Nov 27, 2019
Messages
163
Reaction score
28
For some reason the select function does not change the globals 'richer' and 'poorer' at all. Maybe the difference between a string and a numeric. Don't know, don't care. I changed the call so I can get a return from the function.
I used Number() in the func. to insure I had a number and returned both. Then I change it to a string and found the values. This should be evident for the most part/. The if loop may need to be explained.

The returned value is converted to a string I can obtain the char. at any spot in the string. The highest value for poorer is 9 ( a single digit) so I find the length and take one less because the string numbering starts at 0. Next I could take the char at 0, but it could be 10 and that is two chars - the reason for the loop.
In the
transfer func, you use a different type of array then what you first made and loaded so I just did things to the two variables I had. Check out your array, it's numeric people[1] and people[25], etc.. And each item in the array is set to 100.
Here's the final code:
Code: 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>ginaCoeff</title>
</head>
<body>
<script>
var richer;
var poorer;
var N = 10;
var startLevel = 100;
var people = [];
var trials = 100;
var transferFrac = 0.20;
function loadPeople(N) {
    for (let i = 0; i <= N - 1; i++) {
        people[i] = startLevel;
        //alert(i+', '+ people[i]);
    }
}
function select(N, richer, poorer) {
    var x = Math.floor(Math.random() * N) + 1;
    var y = Math.floor(Math.random() * N) + 1;
    if (x == y) {
        x = x + Math.floor(Math.random() * N) + 1;
        if (x > N) {
            x = x - N;
        }
    }
    richer = Number(Math.max(x, y));
    poorer = Number(Math.min(x, y));
    //alert("fn select: " + "richer " + richer + "  poorer " + poorer);
    return richer+'-'+poorer;
}

function transfer(richer, poorer, transferFrac) {alert(richer);alert(poorer);
    var richer;
    var poorer;
    var transferAmount = poorer * transferFrac;
    richer = richer + transferAmount;
    poorer = poorer - transferAmount;
    alert("fn transfer1: " + "richer " + richer + "  poorer " + poorer);
}

loadPeople(N);
var tiny = select(N, richer, poorer);
tiny.toString();
poorer = tiny.charAt(tiny.length - 1);
if(tiny.length == 4) {
    richer = 10 
}else {
    richer = tiny.charAt(0)
}
transfer(richer, poorer, transferFrac);
//alert(people[richer] + "   " + people[poorer]);
</script>
</body>
</html>
 

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