How to split an array of strings, parse the string numbers as integers and add them together in a for loop

Question

1. I have an array of strings (scores written in the form of fractions) e.g. ["40/60", "30/40", ...]. A score represents a user's response to a question and the array is all of the responses for a given category.

2. I want to split the strings, parse each into an integer, then in a for loop add each left hand side fraction to get a total category score for a user, and add each right hand side fraction to get a total possible max score.

I've already tried the below code and am getting back NaN.

################
var scoreArray = ["45/60", "60/60", "40/40","30/40", "15/20", "30/40", "30/60", "20/40"];

var i;

var myCategoryScore;

var maxCategoryScore;
################

for(i=0; i < scoreArray.length;i++){

    var splitScore = scoreArray[i].split("/");
    console.log(splitScore);

    myQuestionScore = parseInt(splitScore[0], 10);
    myCategoryScore = myCategoryScore + myQuestionScore;
    console.log(myCategoryScore);

    maxQuestionScore = parseInt(splitScore[1]);
    maxCategoryScore = maxCategoryScore + maxQuestionScore; 
    console.log(maxCategoryScore);
}

The result printed is:

Array ["45", "60"]

NaN

NaN

Array ["60", "60"]

NaN

NaN

Array ["40", "40"]

NaN

NaN

etc

However when just printing out the parsed integers on their own its clear they have been correctly parsed...

for(i=0; i<scoreArray.length;i++){

   var splitScore = scoreArray[i].split("/");
   console.log(splitScore);

   myQuestionScore = parseInt(splitScore[0], 10);
   console.log(myQuestionScore);

   maxQuestionScore = parseInt(splitScore[1]);
   console.log(maxQuestionScore);
}

This results in..

Array ["45", "60"]

45

60

Array ["60", "60"]

60

60

Array ["40", "40"]

40

40

etc...

So why can I not add the total together? How do i fix it? Is due to scope?

Thanks!

Answer 1

myCategoryScore is never initialized.

myCategoryScore = myCategoryScore + myQuestionScore; will provide undefined + 42 //NaN

The same for maxCategoryScore

How to reproduce your bug :

var UndefinedValue;

console.log(UndefinedValue);

console.log(UndefinedValue + 42);

Initialize your variables, so you can use them in mathematical operations :

var scoreArray = ["45/60", "60/60", "40/40","30/40", "15/20", "30/40", "30/60", "20/40"];

var i;
// initialize this one
var myCategoryScore = 0;
// and this one
var maxCategoryScore = 0;


for(i=0; i < scoreArray.length;i++){

    var splitScore = scoreArray[i].split("/");
    console.log(splitScore);

    myQuestionScore = parseInt(splitScore[0], 10);
    myCategoryScore = myCategoryScore + myQuestionScore;
    console.log(myCategoryScore);

    maxQuestionScore = parseInt(splitScore[1]);
    maxCategoryScore = maxCategoryScore + maxQuestionScore; 
    console.log(maxCategoryScore);
}