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JavaScript JavaScript Loops, Arrays and Objects Tracking Data Using Objects The Student Record Search Challenge Solution

Posted by yoobin hong
yoobin hong
6,645 Points

I have completed the extra challenge but I'm wondering why this else statement is acting the way it does

So my question is why is the program saying that the student is not in our directory even when the user types in the name of the student who is actually in the directory? I solved the problem looking through the previous asked questions and found the answer to the extra problem but I'm just curious as to why this is the case.

for(var i = 0; i < students.length; i++){ pupil = students[i] if (pupil.name.toUpperCase() === response ) { message += getReport(pupil); found = true; print(message); }else { alert("The student is not in our directory"); break; } }

This is my full script.

var students = [ {name: "Yoobin", track: "Javascript Full stack", achievements: 20, points: 5000 },

{name: "Sarah", track: "Front-end web", achievements: 10, points: 4000 },

{name: "David", track: "PHP", achievements: 50, points: 3000 },

{name: "Chris", track: "Wordpress", achievements: 60, points: 2000 },

{name: "Chris", track: "Ruby on rails", achievements: 100, points: 8000 } ]

var message = ''; var response; var pupil;

function print (message){ var div = document.getElementById('output') div.innerHTML = message; }

function getReport(pupil){ var report = "<h2> Student : " + pupil.name + "</h2>"; report += "<ul><li> Track : " + pupil.track + "</li>"; report += "<li>Achievements : " + pupil.achievements + "</li>"; report += "<li>Points : " + pupil.points + "</li></ul>"; return report; }

while(true){ response = prompt("Type in the name of the student you would like to view their stats on. Type QUIT if you would like to exit the prompt") response = response.toUpperCase();

if(response === null || response==="QUIT"){ break; } for(var i = 0; i < students.length; i++){ pupil = students[i] if (pupil.name.toUpperCase() === response ) { message += getReport(pupil); print(message); }else { alert("The student is not in our directory, Please search again"); break; } } }

2 Answers

andren
andren
28,558 Points

The core of the issue is that it is inside of a loop, the if statement is evaluated for each student that is looped through.

I think it's easiest illustrated by an explanation of what happens behind the scenes when you run the program.

Let's say you type in the name "David", the for loop will pull out the first student from the students array (Yoobin) and then check if that name matches the name you entered, since it does not the else statement runs, since the else statement contains a break keyword the loop then ends right there.

That's the key thing to understand here, all of the students names gets run through that if statement, which means that all of the students whose names do not match the one entered will cause the else clause to trigger if it is placed within the loop. If you removed the break keyword then you would see the alert pop up multiple times as the loop goes through the various student names.

A more robust way to implement a message like that would be to create a Boolean to track whether a student had been found, and then check that Boolean after the loop finished. Like this:

while (true) {
    var wasFound = false; // Bool to track if student(s) was found
    response = prompt("Type in the name of the student you would like to view their stats on. Type QUIT if you would like to exit the prompt")
    response = response.toUpperCase();

    if (response === null || response === "QUIT") {
        break;
    }
    for (var i = 0; i < students.length; i++) {
        pupil = students[i]
        if (pupil.name.toUpperCase() === response) {
            wasFound = true; // Set to true if found
            message += getReport(pupil);
            print(message);
        } 
    }
    if (!wasFound) { // Check if wasFound is false
      alert("The student is not in our directory, Please search again");
    }
}

That is just a quick solution of the top of my head, there are likely other more concise solutions as well.

Nathan Angulo
Nathan Angulo
4,565 Points

I'm having trouble understanding the concept of for in this code. Could you elaborate what the [i] means after "students"?

andren
andren
28,558 Points

Nathan Angulo: That is an example of a for loop.

A for loop takes three expressions within the parenthesis, the first is called the "initializing expression" and whatever you type here is executed once before the loop starts, the second is the "condition" which determines what causes the loop to run in the first place. And the third is called "increment Expression" and this is executed every time the loop has finished a run.

In the code above var i = 0 is the "initializing expression" so when the loop starts a variable called i is created and set to 0. i < students.length is the "condition" so the loop will run as long as i is less than the length of the students array. And i++ is the "increment Expression" so each time the the loop has ran it will increment i by one.

When you place a number in a bracket after an array you tell JavaScript to pull out an item from the array at that index. So students[0] would pull out the item at index 0 (which is the first item), students[1] would pull out the item at index 1 (which is the second item) and so on.

So students[i] will pull out an item from the array. The first time the loop runs i will be 0 so the first student in the students array will be pulled out and assigned to pupil, the second time the loop runs i will be 1 (Since i++ is used as the "increment Expression") so the second student will be pulled, the third time i will be 2 so the third student will be pulled out and so on.

By the time the loop is finished (which happens when i < students.length is no longer true) all of the students will have been pulled out and run through the code within the loop.

yoobin hong
yoobin hong
6,645 Points
yoobin hong
yoobin hong
6,645 Points

Oh!!!! Thank you for the explanation now I get why this code didn't work!! Thank you so much!!!!

Nathan Angulo
Nathan Angulo
4,565 Points

Thank you so much! I think I've finally grasped what's happening in the for loop now in this code. I appreciate it.