Develop Reference

Trying to get values from different arrays to average them

I'm working on this assignment where basically I'm gathering data from users to input their student's grades. I was prompted to store the student names and 4 of each student's grades and average them out in the end. I have hit a hole and unsure how to get these values to add them up and average them.
Here's what I have written so far:
let lab1 = [];
let lab2 = [];
let lab3 = [];
let lab4 = [];
let stuName = [];
let grades = [];
let grade = 0;
let tGrade = 0;
do {
let tName = prompt("Enter Student Name: ");
stuName[stuName.length] = tName;
//prompting user for a grade and converting it LAB1
tGrade = prompt("Input Grade for lab 1: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
lab1[lab1.length] = grade;
}
//prompting user for a grade and converting it LAB2
tGrade = prompt("Input Grade for lab 2: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
lab2[lab2.length] = grade;
}
//prompting user for a grade and converting it LAB3
tGrade = prompt("Input Grade for lab 3: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
lab3[lab3.length] = grade;
}
//prompting user for a grade and converting it LAB4
tGrade = prompt("Input Grade for lab 4: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
lab4[lab4.length] = grade;
}
//giving user option to end inputs
tGrade = prompt("Do you want continue? -1 to exit: ", "-1");
grade = parseInt(tGrade);
} while (grade != -1); //loop escape

Here a solution storing the students with their grades in an object and storing this object in an array. This makes it a bit easier than having 5 different arrays like
let lab2 = [];
let lab3 = [];
let lab4 = [];
let stuName = [];
let grades = [];
To calculate the average you can go then over these objects and build the sum of the grades array and divide it by its length
objStore.forEach((x) => {
let sum = x.grades.reduce((acc, el) => {
acc += el;
return acc;
},0);
console.log(sum / x.grades.length)
})
const objStore = [];
let grade = 0;
let tGrade = 0;
let temp;
do {
temp = {};
let tName = prompt("Enter Student Name: ");
temp["name"] = tName;
temp["grades"] = [];
//prompting user for a grade and converting it LAB1
tGrade = prompt("Input Grade for lab 1: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
temp.grades.push(grade);
}
//prompting user for a grade and converting it LAB2
tGrade = prompt("Input Grade for lab 2: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
temp.grades.push(grade);
}
//prompting user for a grade and converting it LAB3
tGrade = prompt("Input Grade for lab 3: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
temp.grades.push(grade);
}
//prompting user for a grade and converting it LAB4
tGrade = prompt("Input Grade for lab 4: ");
grade = parseInt(tGrade);
//If grade is valid, then add it to the array
if (grade >= 0 && grade <= 100) {
//info stored in the array
temp.grades.push(grade);
}
//giving user option to end inputs
tGrade = prompt("Do you want continue? -1 to exit: ", "-1");
grade = parseInt(tGrade);
objStore.push(temp);
} while (grade != -1); //loop escape
console.log(objStore);
// here we can now calculate the average
objStore.forEach((x) => {
let sum = x.grades.reduce((acc, el) => {
acc += el;
return acc;
},0);
console.log(sum / x.grades.length)
})

I'm assuming you want the average of each student rather than the average of each lab. I've not provided a complete solution because I assume that you'd prefer to have a pointer from which you can figure out more of a solution.
You should be able to loop though the stuName array in such a way that you can use the index of each item in the stuName array to find the corresponding values in the labx arrays.
There are many ways to do this, but a for loop, Array.forEach or Array.map should allow you to do this. (For Array.forEach and Array.map) the callback's second argument is the current index of the item in the array.
Example usage of Array.forEach:
const students = ['Neera', 'Erik', 'Dolly'];
const student_score = [2, 5, 6];
students.forEach((name, index) => console.log('Name: ' + name + ' has score ' + student_score[index]));

Using JS i need to create a Average variable

hi i need to create a Average variable that will average out my grades any help will be greatly appreciated i have the following. but i cant figure out the average portion of it
my code works for the inputs and gets the grades, and i also have the html portion
and i have an empty p tag for all of the inner html
function myFunction(){
let math = document.getElementById("math").value;
let science = document.getElementById("science").value;
let history = document.getElementById("history").value;
let english = document.getElementById("english").value;
let average = ( [ "math","science","history","english", ] );
// this is match sec
if(math >= 90) {
document.getElementById("mathG").innerHTML = "Your Grade is A"
}
else if (math >= 80 && math < 90) {
document.getElementById("mathG").innerHTML = "Your Grade is B"
}
else if (math >= 70 && math < 80) {
document.getElementById("mathG").innerHTML = "Your Grade is c"
}
else if (math >= 60 && math < 70) {
document.getElementById("mathG").innerHTML = "Your Grade is d"
}
else {
document.getElementById("mathG").innerHTML = "Your Grade is F"
}
// Science section
if(science >= 90) {
document.getElementById("scienceG").innerHTML = "Your Grade is A"
}
else if (science >= 80 && science < 90) {
document.getElementById("scienceG").innerHTML = "Your Grade is B"
}
else if (science >= 70 && science < 80) {
document.getElementById("scienceG").innerHTML = "Your Grade is c"
}
else if (science >= 60 && science < 70) {
document.getElementById("scienceG").innerHTML = "Your Grade is d"
}
else {
document.getElementById("scienceG").innerHTML = "Your Grade is F"
}
// History
if(history >= 90) {
document.getElementById("historyG").innerHTML = "Your Grade is A"
}
else if (history >= 80 && history < 90) {
document.getElementById("historyG").innerHTML = "Your Grade is B"
}
else if (history >= 70 && history < 80) {
document.getElementById("historyG").innerHTML = "Your Grade is c"
}
else if (history >= 60 && history < 70) {
document.getElementById("historyG").innerHTML = "Your Grade is d"
}
else {
document.getElementById("historyG").innerHTML = "Your Grade is F"
}
//English
english
if(english >= 90) {
document.getElementById("englishG").innerHTML = "Your Grade is A"
}
else if (english >= 80 && english < 90) {
document.getElementById("englishG").innerHTML = "Your Grade is B"
}
else if (english >= 70 && english < 80) {
document.getElementById("englishG").innerHTML = "Your Grade is c"
}
else if (english >= 60 && english < 70) {
document.getElementById("englishG").innerHTML = "Your Grade is d"
}
else {
document.getElementById("englishG").innerHTML = "Your Grade is F"
}

The code will be like this I guess :
let average = math + science + history + english / 4;
Here you will get the average and with the if else like you did for getting grades for each subject you can find the average grade as well.
if(average >= 90) {
average = "A";
}
Tip: You can use loop or map to reduce the line of code.

A few things:
First, make sure to cast your inputs to a number. It works with strings when doing a comparison with > or <, but if you try to add strings together with +, it will concatenate them rather then summing their numeric values.
Second, you can shorten your code by putting the duplicated if/else chains into a function.
Anyway, an average is just a sum divided by the number of summed items, so:
let average = (math + science + history + english) / 4;
would work. Or you can use a reduce if you have them in an array. This might come in handy if you frequently add or remove subjects:
let scores = [math, science, history, english];
let average = scores.reduce((total, score) => total + score) / scores.length;
Anyway, here's a snippet that seems to be working how you want:
function calculateAllGrades() {
let math = Number(document.getElementById("math").value);
let science = Number(document.getElementById("science").value);
let history = Number(document.getElementById("history").value);
let english = Number(document.getElementById("english").value);
// let average = ( [ "math","science","history","english", ] );
// Hardcoded, okay if these are all subjects:
let average = (math + science + history + english) / 4;
// Or if they change, you can use an array, easier if they change or you add more:
let scores = [math, science, history, english]
average = scores.reduce((sum, score) => sum + score) / scores.length
function calculateGrade(score, elementID) {
const element = document.getElementById(elementID);
if (score >= 90) {
element.innerHTML = "Your Grade is A";
} else if (score >= 80) {
element.innerHTML = "Your Grade is B";
} else if (score >= 70) {
element.innerHTML = "Your Grade is C";
} else if (score >= 60) {
element.innerHTML = "Your Grade is D";
} else {
element.innerHTML = "Your Grade is F";
}
}
calculateGrade(math, "mathG")
calculateGrade(science, "scienceG")
calculateGrade(history, "historyG")
calculateGrade(english, "englishG")
calculateGrade(average, "averageG")
}
let button = document.getElementById("button")
button.addEventListener("click", calculateAllGrades)
<div>MATH:<input type="text" id="math" /></div>
<div>SCIENCE:<input type="text" id="science" /></div>
<div>HISTORY:<input type="text" id="history" /></div>
<div>ENGLISH:<input type="text" id="english" /></div>
<br />
<div>MATH:<div id="mathG"></div></div><br/>
<div>SCIENCE:<div id="scienceG"></div></div><br/>
<div>HISTORY:<div id="historyG"></div></div><br/>
<div>ENGLISH:<div id="englishG"></div></div><br/>
<div>AVERAGE:<div id="averageG"></div></div><br/>
<button id="button">Calculate</button>

history is a global in browsers, so you can't use it as a variable name.
You should do something like:
let mathGrade = document.getElementById("math").value;
let scienceGrade = document.getElementById("science").value;
let historyGrade = document.getElementById("history").value;
let englishGrade = document.getElementById("english").value;
let average = (mathGrade + scienceGrade + historyGrade + englishGrade) / 4
Then, if you want the 'average' letter grade, you can do something similar to what you did for the other grades using the average:
if(average >= 90) {
document.getElementById("averageG").innerHTML = "Your Average Grade is A"
}
else if (average >= 80 && average < 90) {
document.getElementById("averageG").innerHTML = "Your Average Grade is B"
}
else if (average >= 70 && average < 80) {
document.getElementById("averageG").innerHTML = "Your Average Grade is c"
}
else if (average >= 60 && average < 70) {
document.getElementById("averageG").innerHTML = "Your Average Grade is d"
}
else {
document.getElementById("averageG").innerHTML = "Your Average Grade is F"
}

Codewars: Grasshopper - Grade book challenge

This is one of those times where the solution is staring me right in the face but I can't seem to find it! So please be patient with me. The kata instruction is the following:
Complete the function so that it finds the mean of the three scores passed to it and returns the letter value associated with that grade.
Numerical Score Letter Grade
90 <= score <= 100 'A'
80 <= score < 90 'B'
70 <= score < 80 'C'
60 <= score < 70 'D'
0 <= score < 60 'F'
Tested values are all between 0 and 100. There is no need to check for negative values or values greater than 100.
Here is my solution:
function getGrade (s1, s2, s3) {
var score = (s1 + s2 + s3) / 3;
if (90 <= score && score >= 100) {
return 'A';
} else if (80 <= score && score > 90) {
return 'B';
} else if (70 <= score && score > 80) {
return 'C';
} else if (60 <= score && score > 70) {
return 'D';
} else if (0 <= score && score > 60) {
return 'F';
}
}
getGrade(5,40,93);
getGrade(30,85,96);
getGrade(92,70,40);
Can't for the life of me figure out what I am doing wrong.

Your conditions in if statement are all wrong. These are the right conditions
function getGrade (s1, s2, s3) {
var score = (s1 + s2 + s3) / 3;
if (score >= 90 && score <= 100) {
return 'A';
} else if (score >= 80 && score < 90) {
return 'B';
} else if (score >= 70&& score < 80) {
return 'C';
} else if (score >= 60 && score < 70) {
return 'D';
} else {
return 'F';
}
}

your conditions are wrong and you don't need multiple check in same if .Change your code to this:
function getGrade (s1, s2, s3) {
var score = (s1 + s2 + s3) / 3;
if (score >= 90 && score <= 100) {
return 'A';
} else if (score >= 80 ) {
return 'B';
} else if (score >= 70 ) {
return 'C';
} else if (score >= 60) {
return 'D';
} else{
return 'F';
}
}
console.log(getGrade(5,40,93));
console.log(getGrade(30,85,96));
console.log(getGrade(92,70,40));

You could use only if clauses without else parts and check only the lower bound, because you have already checked the upper bound.
The check for upper 100 is missing, because your given range is between 0 and 100.
function getGrade(s1, s2, s3) {
var score = (s1 + s2 + s3) / 3;
if (score >= 90) {
return 'A';
}
if (score >= 80) {
return 'B';
}
if (score >= 70) {
return 'C';
}
if (score >= 60) {
return 'D';
}
return 'F';
}
console.log(getGrade(5, 40, 93));
console.log(getGrade(30, 85, 96));
console.log(getGrade(92, 70, 40));

Whenever you find yourself writing long chains of if-else statements, see if you can find a pattern and use a lookup table. Here, we have only 5 grade buckets, but what if we had 20 or 100? You can see the if-else approach isn't scalable.
In this case, if we use the string "FFFFFFDCBAA" then we've enumerated all 5 grade buckets in a way that lets us index into after dividing the score by 10. The code for that would be: "FFFFFFDCBAA"[score/10|0] where | 0 is the floor operation, chopping off the decimal. The extra "A" handles the case of 100.
Secondly, the arguments to the function (s1, s2, s3) make no sense. Why 3 scores? If we have 4 score, or 20 scores, the function can't be used and we have to rewrite the whole function with the right number of arguments (and the 20-argument one will be pretty ugly). I realize this header is what the kata author gave you, but there's no reason we can't make it handle any number of arguments using (...args) and still pass the tests. If we take the average of the arguments using args.reduce((a, e) => a + e, 0) / args.length, we're left with the following solution:
const sum = a => a.reduce((a, e) => a + e, 0);
const avg = a => sum(a) / a.length;
const getGrade = (...args) => "FFFFFFDCBAA"[avg(args)/10|0];
[
[0],
[0, 100, 50],
[90, 95, 100],
[80, 60],
[81, 79],
[80, 59],
].forEach(test => console.log(`${test} => ${getGrade(...test)}`));

Trying to find the average

I need to know why when I try to divide student 1,student 2 and student 3. I think it might be a looping error since the number that it give's me is numbering in the thousands but I don't see how that could be happening.
function averageOfThreeScores() {
var student1;
var student2;
var student3;
var end;
do {
student1 = prompt("What are the scorces of students 1?");
student2 = prompt("What are the scorces of students 2?");
student3 = prompt("What are the scorces of students 3?");
end = prompt("Would you like to end, type yes to end.");
var average = (student1 + student2 + student3) / 3;
if (average <= 59) {
document.write(average + " Your score is F <br/>");
} else if (average <= 69) {
document.write(average + " Your score is D <br/>");
} else if (average <= 79) {
document.write(average + " Your score is C <br/>");
} else if (average <= 95) {
document.write(average + "That's a great score <br/>");
} else if (average <= 100) {
document.write(average + "God like </br>");
} else {
document.write(average + " End <br/>");
}
}
while (end != "yes");
}

You expect the sum of student grades to be number but in fact they are concatenated as string. So if user types following values for example:
for student1: 13
for student2: 36
for student3: 50
The average will be 44550 because the sum will be (concatenated strings): 133650
To fix this, just convert the type to number when you get it.
student1 = parseInt(prompt("What are the scorces of students 1?"));
student2 = parseInt(prompt("What are the scorces of students 2?"));
student3 = parseInt(prompt("What are the scorces of students 3?"));

Find the sum of a Javascript array and divide by its length

I'm almost embarrassed to ask this.
I'm a beginner programmer, and Javascript is very confusing to me. I managed to put together this much with the help of my instructor, but there are some simple things I can't get right.
I tried search Stack Overflow for a thread that would answer my question, but all of them I've seen contain code that I haven't learned about yet, so they're all just gibberish to me.
What I'm trying to do is add all the values of an Array and divide the sum by the array's length, ergo, find the average. The description of the assignment is find the average of any number of students' grades.
My two problems are
I can't figure out how to get the sum of all numeric values in the Array and,
For some reason, array.length returns one more than the actual length of the Array, even if I add a -1. (ex. if I enter 6 values, the array.length would return 7.)
I know where the problem is but I can't figure out what I need to enter. This assignment is due tomorrow, so anyone's time and effort is appreciated.
Here is my script:
<script type="text/javascript">
var allGrades = new Array();
var g = 0;
var l = 0;
var s = 0;
var t = 0;
do {
allGrades[g] = window.prompt("Please enter one grade for each window. After you enter a grade, enter an 'x' to see the average of the grades you entered.", "")
g++;
}
while (allGrades[g - 1] != "x")
for (l = 0; l < allGrades.length - 1; l++) {
s += allGrades[l] // Where I think the problem is
}
t == s / g - 1;
g == allGrades.length - 1; //
window.alert(g)
switch (t) {
case (t >= 90):
window.alert("Your average grade is " + (t) + ". " + "This is an A.")
break;
case (t >= 80 && t < 90):
window.alert("Your average grade is " + (t) + ". " + "This is a B.")
break;
case (t >= 70 && t < 80):
window.alert("Your average grade is " + (t) + ". " + "This is a C.")
break;
case (t >= 60 && t < 70):
window.alert("Your average grade is " + (t) + ". " + "This is a D.")
break;
case (t <= 60):
window.alert("Your average grade is " + (t) + ". " + "This is a failing grade.")
break;
}
</script>
I'm sorry if what I'm asking seems dumb. I've only been taking web programming for about two months, so I could really use some help!
Kyle

== is the comparison operator. You need to use the assignment operator (=) here:
t==s/g-1;
And the lines near it.
Also, for your own sake, do not use single-letter variable names unless you have a good reason for doing so.
Here's a cleaner way of writing the script:
var grades = [];
do {
var input = window.prompt("Please enter one grade for each window. After you enter a grade, enter an 'x' to see the average of the grades you entered.", "");
grades.push(parseFloat(input));
} while (input != 'x');
var sum = 0;
for (int i = 0; i < grades.length; i++) {
sum += grades[l];
}
var average = (sum / grades.length) * 100;
var grade;
if (average >= 90) {
grade = 'A';
} else if (average >= 80) {
grade = 'B';
} else if (average >= 70) {
grade = 'C';
} else if (average >= 60) {
grade = 'D';
} else {
grade = 'failing grade';
}
alert('Your average grade is ' + average + '. ' + 'This is a ' + grade);

t==s/g-1;
g==allGrades.length-1; //
Are both Comparisons, for assignment they should be
t=s/g-1;
g=allGrades.length-1;