3.1 - While
Repeat, Repeat, Repeat, Repeat...
Review
We can do the following with code:
control input & output
store values and manipulate them
control code with if-statements
"chunk" code in functions that run when commanded.
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Repeating code is inefficient. And what if we don't know when it should end?
// Ask the user to enter a number and check for valid input
let input = Number(prompt(“Enter a number.”));
if (isNaN(input))
input = Number(prompt(“Please enter a number.”));
if (isNaN(input))
input = Number(prompt(“Ugh, please enter a number.”));
if (isNaN(input))
input = Number(prompt(“Enter a NUMBER.”));
if (isNaN(input))
...
The ability to repeat, or loop, code provides lots of possibilities. The first loop we will look at is called the while loop and acts a lot like an if-statement.
// Example: A never-ending loop (not good)
while (true) {
console.log("You can't stop me!");
}
// Example: Counting to 10
let n = 0;
while (n <= 10) {
console.log("n is", n);
n++; // We need to make sure we modify 'n'!
}
// Example: Should I stop?
let input = "n";
while (input.toUpperCase() != "Y") {
input = prompt("Should I stop? (y/n)");
}
console.log("Ok, I stopped");
Some Resources
Scrimba demo on While Loops (recorded live in a previous class)
Today's Task(s) / Homework