n301/cs19loops n301.tplt Loops
Allows certain parts of code to repeat based on the status of a condition

The while statement.
The while statement checks the condition and repeats the code if the condition is TRUE. Sentry variables and Initialization Start by creating a variable Giving the variable an initial value is initializing the variable Variables used in loops are often known as sentry variables Math Quiz Ask the user a simple math question. Continue asking the question until the user gets the answer correct. Preventing Endless Loops Inside a loop, we MUST ensure that there is some way of exiting the loop We have to make it possible for the sentry variable to change values Example  var stillRacing = "Y";

 while (stillRacing == "Y"){
   alert("zooming around the track");

   //forgot to check if we are still racing!!!

 }// end while
 alert ("Nice race!!");
This program will go on FOREVER!!! Endless Loops The condition statement checks to see if the condition is TRUE In the previous example, the condition is true Because the condition is true, the body of the loop still thinks we are "zooming around the track" Whenever you make a loop, it is your obligation to ensure that the sentry variable is changed so it is possible to exit the loop The For Loop Variation of the loop we have already used Difference - we have added a counter Needs four pieces of information:
 - name of counting variable
 - starting value of the variable
 - ending value of the variable
 - how to increment the variable For Loop The for statement needs three parts:
 1.  initialize the variable
 2.  a condition
 3.  how to increment the variable Once the loop is set up, we don't have to worry about it in the body - it automatically increments Ten Lap Race Simulate a race with a program that says "now on lap: " for ten laps. Backwards Race Write a program that goes from ten to one Mad lib Try this one on your own. Ask the user for a number of words (favorite color, name of a person, adjective). Use these words in a story.