# Thread: Sum the numbers of an array

1. Shi
Registered User
Join Date
Apr 2017
Posts
14

## Sum the numbers of an array

Hello!

I wrote a function that should sum up all the numbers that are contained within an array which just was created.
In the mySum function I use the variable "sumOfNumbers" to count all the numbers together. But I do get out NaN.

I checked with typeof, the array is an array(object), the numbers I extract are numbers, the "sumOfNumbers" variable I created as a number. Why is it not able to count the numbers to the variable?
I tried to use Number() to make sure what is counted together are numbers, but does not seem to work.

Code:
// range to array
function myRange(start, end) {
var numberList = [];

for (var i = start; i <= end; i++) {
numberList[i] = i;
}
return numberList;
}

//sum array numbers
function mySum(numbers) {
var numbers = numbers;
var sumOfNumbers = 0;

for (var i = 0; i <= numbers.length-1; i++) {
var c = numbers[i];
sumOfNumbers += c;   <-- becomes NaN
}
return sumOfNumbers;
}

var x = mySum(myRange(5, 7));
console.log(x);

2. Registered User
Join Date
Mar 2011
Posts
124
It doesn't work because
Code:
// range to array
function myRange(start, end) {
var numberList = [];
for (var i = start; i <= end; i++) {
numberList[i] = i;			// <-- start at position i
}
return numberList;
};

var arr = myRange(5, 7);			// arr = [undefined,undefined,undefined,undefined,undefined,5,6,7]
mySum(arr);

function mySum(numbers) {
var numbers = numbers;
var sumOfNumbers = 0;

for (var i = 0; i <= numbers.length-1; i++) {
var c = numbers[i];
sumOfNumbers += c;   //<-- becomes NaN, because adding to undefined
}
return sumOfNumbers;
};
This does what you want
Code:
function myRange(start, end) {
var numberList = [];
for (var i = start; i <= end; i++) {
numberList.push(i);
}
return numberList;
};

function mySum(numbers) {
var sumOfNumbers = 0;
for (var i = 0; i < numbers.length; i++) {
sumOfNumbers += numbers[i];
}
return sumOfNumbers;
};

var arr = myRange(5, 7);
mySum(arr);

3. or prototype it...

Code:
Array.prototype.array_sum = function(){
// sum the array elements 0 to nth, does not count associative named arrays
for( this['sum']=0, tc=0; tc<this.length; tc++ ) this['sum'] += this[tc];
this['count'] = this.length;
}
Then use it like...

myArray.array_sum();
then to get the sum of it, you use sum = myArray['sum'];

Code:
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
arr.array_sum();
console.log("> " + arr + " = " + arr['sum'] );
outputs to the console log (F12 open close, click console log tab )
Code:
> 1,2,3,4,5,6,7,8,9,10 = 55

4. Shi
Registered User
Join Date
Apr 2017
Posts
14
Thank you very much for your answers. This helped.

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