Arrays properties and methods practice

Question

Can any one please tell me why this one doesn't work:

function main() {
//take the number of passed levels
var levels = parseInt(readLine(),10);
var points = new Array();

var count = 0;
while(count<levels){
var elem = parseInt(readLine(),10);
points[count] = elem;
count++;
}

var sum = 0;
//calculate the sum of points
while(count!=0)
{
sum += points[count];
count--
}

//output
console.log(sum);
}

but this one does?

function main() {
//take the number of passed levels
var levels = parseInt(readLine(),10);
var points = new Array();

var count = 0;
while(count<levels){
var elem = parseInt(readLine(),10);
points[count] = elem;
count++;
}

var sum = 0;
//calculate the sum of points
a = 0;
while(a<points.length)
{
sum += points[a];
a++
}

//output
console.log(sum);
}

Answer 1

Marc Andrew Picardal ,

Please add a tag for the language.

Answer 2

Marc Andrew Picardal the first code mistakenly uses count as the array index whereas it should be count-1.

I would recommend moving up count--, so it happens before using count as the index.

count--;
sum += points[count];

or try this

sum += points[--count];