74 lines
2.4 KiB
Markdown
74 lines
2.4 KiB
Markdown
---
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id: 587d7b86367417b2b2512b3d
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title: Prevent Infinite Loops with a Valid Terminal Condition
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challengeType: 1
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forumTopicId: 301192
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---
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## Description
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<section id='description'>
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The final topic is the dreaded infinite loop. Loops are great tools when you need your program to run a code block a certain number of times or until a condition is met, but they need a terminal condition that ends the looping. Infinite loops are likely to freeze or crash the browser, and cause general program execution mayhem, which no one wants.
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There was an example of an infinite loop in the introduction to this section - it had no terminal condition to break out of the <code>while</code> loop inside <code>loopy()</code>. Do NOT call this function!
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```js
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function loopy() {
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while(true) {
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console.log("Hello, world!");
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}
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}
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```
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It's the programmer's job to ensure that the terminal condition, which tells the program when to break out of the loop code, is eventually reached. One error is incrementing or decrementing a counter variable in the wrong direction from the terminal condition. Another one is accidentally resetting a counter or index variable within the loop code, instead of incrementing or decrementing it.
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</section>
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## Instructions
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<section id='instructions'>
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The <code>myFunc()</code> function contains an infinite loop because the terminal condition <code>i != 4</code> will never evaluate to <code>false</code> (and break the looping) - <code>i</code> will increment by 2 each pass, and jump right over 4 since <code>i</code> is odd to start. Fix the comparison operator in the terminal condition so the loop only runs for <code>i</code> less than or equal to 4.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: Your code should change the comparison operator in the terminal condition (the middle part) of the <code>for</code> loop.
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testString: assert(code.match(/i\s*?<=\s*?4;/g).length == 1);
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- text: Your code should fix the comparison operator in the terminal condition of the loop.
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testString: assert(!code.match(/i\s*?!=\s*?4;/g));
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function myFunc() {
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for (let i = 1; i != 4; i += 2) {
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console.log("Still going!");
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}
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}
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function myFunc() {
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for (let i = 1; i <= 4; i += 2) {
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console.log("Still going!");
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}
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}
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```
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</section>
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