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);

• user2417483: 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.
• Barmar: 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.
• Dwza: looping to 2200 with max 10 steps per run and 3 alerts is really not recommended :) this would be 660 alerts to do... :S

Answer 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.

• jaramore: Okay, I changed it and it's still asking the question one time.
• Dwza: 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: @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: 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 ^^

Answer 2

there seem to be multiple problems :

1. 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.

2. make sure you parseInt from the prompt response.

3. 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);

• user3241019: 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.
• daksh_019: @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.

Answer 3

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 !