Basic Loops

While Loop

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The while loop is the simplest and most frequently used loop. It consists of a loop condition that determines the number of times the while loop executes a block of statements. The loop condition is usually an expression that evaluates to true or false. However, if you recall our previous discussion of true-like and false-like values, the expression could technically be of any data type. Non-zero numbers such 3 or 5 are evaluated as true while 0 is evaluated as false. Other data types also have similar cases whereas the value itself can be expressed as a true or false value.

The while loop above prints the numbers from 1 to 10 in order to the console. Let's take a look at how this works. The loop condition is the expression inside the brackets, in this case, counter < 11. As long as the expression is true, the statements inside the while loop will be repeatedly executed. The value of counter starts as 1, and continues to increase by one after the while loop is executed.

After the first run of the while loop, the value of counter is 2 and the while loop will keep running until counter is 11. This is because "11 < 11" is false, which is why the while loop will stop running. If the statement counter+=1 does not exist, the value of counter will always be 1, causing the while loop to run infinitely, causing an infinite loop.

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Application Question

Consider the following code segment:

let varOne = 15;
            while (varOne < 28){
                console.log(varOne);
                varOne++;
            }
            

What are the first and last numbers printed on the console after running the code above?