Jump to the task

The while loop works on a condition (or multiple conditions)

while ((x <= 5) && (paused == false)) {   
  // do something
}

A lot of the time, it involves a counting variable - doing the loop a certain number of times

while (count < 100) {
  // do something
}

But many programmers forget to modify the counting variable, causing an infinite loop!

If you know you'll be counting - maybe going through a string or list - you could use the for loop.

for (part1; part2; part3) { 
  // Your code
}

• part1 is the declaration of any indexer or counting variable. Example: let i = 0;
• part2 is exactly like the while condition. Example: i < 10; (which means while i is less than 10)
• part3 is what will happen to the indexer on each loop iteration. Example: i++ (increase i by 1) or maybe i += 3 (add 3 to i) on each iteration

for (let i = 100; i > 0; i--) {
  // Count down from 100 to 1
}

for (let j = 10; j <= 30; j += 2) {
  // Count up by 2's from 10 to 30
}

for (let x = 93; x > 51; x -= 5) {
  // Count down by 5's from 93 to 51
}

Print from 0% to 100% going up by 2.5%

for (let p = 0; p <= 100; p += 2.5) {
  console.log(p + "%");
}

// Output:
0%
2.5%
5%
...
97.5%
100%

Print the alphabet on one line using the character codes:

let alpha = "";

for (let letter = 65; letter < 91; letter++) {
  alpha += String.fromCharCode(letter);
}

console.log(alpha);
// Prints ABCDEFGHIJKLMNOPQRSTUVWXYZ

Return to the lesson

Make a new coding file called 3.3 - For Loops.js. Complete the following in that file. Assume the function parameters are proper numbers (no need for error-checking).

1. Write the function countUp(start, stop) that prints from start to stop (inclusive) on the console. Example:

> countUp(5, 8)
5
6
7
8

2. Write the function countDown(start, stop) that prints down from start to stop on the console. Example:

> countDown(10, 6)
10
9
7
6

1. Write the function sum(n) which returns the sum (addition) from 1 to n. Use a for-loop to complete it.
   For Example: sum(7) returns 28 (because 1+2+3+4+5+6+7 = 28)
   
   

2. Write the function count4(begin, end) that returns how many numbers are divisible by 4 from begin to end (inclusive). Use a for-loop to complete it.
   For Example: count4(5, 43) returns 9 (because 8, 12, 16, 20, 24, 28, 32, 36, 40)
   
   

3. Write the function sum_divisible(n, x) which returns the sum (addition) of the values from 0 to n that are divisible by x.
   For Example: sum_divisible(32, 6) returns 90 (because 6+12+18+24+30 = 90)