Do While Loop in Javascript

Question

I have a problem in my loop. I want to keep asking the user which ticket type to purchase and how many they would like to buy until MAX_SEAT_COUNT <= totTickets. My code would only run through the questions once. MAX_SEAT_COUNT = 2200

        do {
            ticketType = prompt ("Ticket Types: Toddlers = 1  Juniors = 2  Adults = 3 Please enter a ticket type: 1, 2, 3", "");
            if (ticketType == 1) {
                manyToddlers = prompt ("How many toddler tickets are you purchasing? You can only buy 10 tickets per ticket type.", "");
            } else if (ticketType == 2) {
                manyJuniors = prompt ("How many junior tickets are you purchasing? You can only buy 10 tickets per ticket type.", "");                  
            } else if (ticketType == 3) {
                manyAdults = prompt ("How many adult tickets are you purchasing? You can only buy 10 tickets per ticket type.", "");        
            } else {
                alert ("Please enter the correct number for each ticket type.");
            }

                if (manyToddlers <= 10) {
                    toddlersCounter = toddlersCounter + manyToddlers;
                    costToddlers = manyToddlers * toddlers;
                    alert ("You bought " + manyToddlers + " toddler tickets for $ " + costToddlers.toFixed(2)); 
                } else if (manyJuniors <= 10) {
                    juniorsCounter = juniorsCounter + manyJuniors;
                    costJuniors = manyJuniors * juniors;
                    alert ("You bought " + manyJuniors + " junior tickets for $ " + costJuniors.toFixed(2));    
                } else if (manyAdults <= 10) {
                    adultsCounter = adultsCounter + manyAdults;
                    costAdults = manyAdults * adults;
                    alert ("You bought " + manyAdults + " adult tickets for $ " + costAdults.toFixed(2));   
                } else {
                    alert ("You can only buy 10 tickets per ticket type.");
                }

        totTickets = toddlersCounter + juniorsCounter + adultsCounter;
        totSales = costToddlers + costJuniors + costAdults;     

        } while (MAX_SEAT_COUNT <= totTickets);

The prompt command always returns a string value so you should convert these text numbers to proper numerals by manyToddlers = parseInt( manyToddlers,10). The maths may also work as expected. — user2417483
– user2417483, Commented Sep 25, 2014 at 6:52
Don't you have the condition backwards? You should loop while the number of tickets is less than the maximum, not while it's greater. — Barmar
– Barmar, Commented Sep 25, 2014 at 6:52
looping to 2200 with max 10 steps per run and 3 alerts is really not recommended :) this would be 660 alerts to do... :S — Dwza
– Dwza, Commented Sep 25, 2014 at 7:55

Barmar · Accepted Answer · 2014-09-25 06:54:27Z

1

Your while condition is wrong. It should be:

while (totTickets <= MAX_SEAT_COUNT)

The loop is only running once because your condition is failing after the first loop.

answered Sep 25, 2014 at 6:54

Barmar

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4 Comments

jaramore Over a year ago

Okay, I changed it and it's still asking the question one time.

Dwza Over a year ago

Actually it doesn't matter if he uses while or do-while. The only difference is, the do-while goes through the process at least once and while firt checks conditions. And atm i can't see where he stores the data so the loop will allways start from beginning. That's the reason why it doesn't matters :)

Barmar Over a year ago

@Dwza I didn't say anything about whether it should be while or do-while. My change is that it should be totTickets <= MAX_SEAT_COUNT, not MAX_SEAT_COUNT <= totTickets

Dwza Over a year ago

hmm, i could swear i read some about use while not do while ^^ may i am working to long and read to much that my brain is faking me ^^

daksh_019 · Accepted Answer · 2014-09-25 07:55:36Z

there seem to be multiple problems :

Define all your variables and set them to a default value of 0 (or what suits you) before using them. For example if I choose adult type(3) in the first prompt, then variables manyToddlers and manyJuniors will remain undefined and now the second if(){} will throw an error of undefined in the operations.
make sure you parseInt from the prompt response.
change your while condition to totTickets <= MAX_SEAT_COUNT;

only as an example the code below should work fine , however i recommend you do it in a better way keeping all things clear and defined:

manyToddlers = 0;
    manyJuniors = 0;
    manyAdults = 0;

    toddlersCounter = 0;
    toddlers = 0;
    costToddlers = 0;

    juniorsCounter = 0;
    manyJuniors = 0;
    juniors =0;
    costJuniors = 0;

    adultsCounter = 0;
    costAdults = 0;
    adults = 0;

    totTickets = 0;
    MAX_SEAT_COUNT = 10;
    do {
        ticketType = prompt ("Ticket Types: Toddlers = 1  Juniors = 2  Adults = 3 Please enter a ticket type: 1, 2, 3", "");
        if (ticketType == 1) {
            manyToddlers = prompt ("How many toddler tickets are you purchasing? You can only buy 10 tickets per ticket type.", "");
        } else if (ticketType == 2) {
            manyJuniors = prompt ("How many junior tickets are you purchasing? You can only buy 10 tickets per ticket type.", "");
        } else if (ticketType == 3) {
            manyAdults = prompt ("How many adult tickets are you purchasing? You can only buy 10 tickets per ticket type.", "");
        } else {
            alert ("Please enter the correct number for each ticket type.");
        }

        manyToddlers = parseInt(manyToddlers,10);
        manyJuniors = parseInt(manyJuniors,10);
        manyAdults = parseInt(manyAdults,10);

        if (manyToddlers <= 10) {
            toddlersCounter = toddlersCounter + manyToddlers;
            costToddlers = manyToddlers * toddlers;
            alert ("You bought " + manyToddlers + " toddler tickets for $ " + costToddlers.toFixed(2));
        } else if (manyJuniors <= 10) {
            juniorsCounter = juniorsCounter + manyJuniors;
            costJuniors = manyJuniors * juniors;
            alert ("You bought " + manyJuniors + " junior tickets for $ " + costJuniors.toFixed(2));
        } else if (manyAdults <= 10) {
            adultsCounter = adultsCounter + manyAdults;
            costAdults = manyAdults * adults;
            alert ("You bought " + manyAdults + " adult tickets for $ " + costAdults.toFixed(2));
        } else {
            alert ("You can only buy 10 tickets per ticket type.");
        }

        totTickets = toddlersCounter + juniorsCounter + adultsCounter;
        totSales = costToddlers + costJuniors + costAdults;

    } while (totTickets <= MAX_SEAT_COUNT);

You won't get to 2200 if you keep this totTickets = toddlersCounter + juniorsCounter + adultsCounter;, and if you don't reset those vars except totTickets you will reach it in a few loops.
@user3241019 : I acknowledge and agree with what you say. This was supposed to be a help with the do while looping and so I set the MAX_TICKETS to ten. As for the actual program, a lot of improvements are required. For a start variables in loop are not required to be global and of course this is not a good way of actual ticket booking/marking system.

user3241019 · Accepted Answer · 2014-09-26 06:14:14Z

I changed your code a bit, to get it easier to read, and make it work as well. Your problem was in the structure of your while :

Handle the user input if it's not 1, 2, or 3
Get the right tickets count at the end
Correctly loop while totTickets <= MAX...

Here is a sample of the structure if you want to have a look :

if (manyAdults <= 10) {
   adultsCounter = adultsCounter + manyAdults;
   costAdults = manyAdults * adults;
   alert("You bought " + manyAdults + " adult tickets for $ " + costAdults.toFixed(2));
} else {
   alert("You can only buy 10 tickets per ticket type.");
}

totTickets = totTickets + toddlersCounter + juniorsCounter + adultsCounter;
//don't forget to reset their values, otherwise your ticket count will grow instantly               
toddlersCounter = 0; juniorsCounter = 0; adultsCounter = 0;
totSales = costToddlers + costJuniors + costAdults;

I put a button in the Fiddle to control the launch of your while :)

Take a look at this Working Fiddle with the entire code !

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