Grouping cases and negation

Sometimes different values need the same action. In this program "sunny" and "cloudy" print the same sentence, so three lines are repeated for nothing:

JavaScript

const weather = "cloudy";

switch (weather) {
  case "sunny":
    console.log("Let's go shopping");
    break;
  case "cloudy":
    console.log("Let's go shopping");
    break;
  case "rainy":
    console.log("Let's stay home");
    break;
}

Console

Let's go shopping

The fix: write the cases one after another, then the action once. In a target game, hitting 4 or 8 wins a video game, 1 or 7 wins candy, anything else a sticker:

JavaScript

const target = 7;

switch (target) {
  case 4:
  case 8:
    console.log("Get video game");
    break;
  case 1:
  case 7:
    console.log("Get candy assortment");
    break;
  default:
    console.log("Get sticker");
    break;
}

Console

Get candy assortment

Grouping works because case 1: has no break, so the program runs on to the lines after case 7:. We used const instead of let because the target number never changes after it is hit; const declares a variable whose value cannot change.

Taking turns with the remainder

Students go into 4 groups in turn: the first in A, the second in B, the third in C, the fourth in D, then the fifth back in A. The remainder after dividing by 4 repeats in the same pattern, so 4 cases cover any number:

Student number	1	2	3	4	5	6	7	8
num % 4	1	2	3	0	1	2	3	0
Group	A	B	C	D	A	B	C	D

JavaScript

const num = 6;

switch (num % 4) {
  case 1:
    console.log("Student " + num + " is in Group A");
    break;
  case 2:
    console.log("Student " + num + " is in Group B");
    break;
  case 3:
    console.log("Student " + num + " is in Group C");
    break;
  case 0:
    console.log("Student " + num + " is in Group D");
    break;
}

Console

Student 6 is in Group B

Negation with !

Putting ! before a condition flips its result: true becomes false and false becomes true. Put the condition in brackets with ! in front, and it means "if it is not…":

JavaScript

console.log(5 > 3);
console.log(!(5 > 3));

let seat = "sold out";
if (!(seat == "available")) {
  console.log("It's sold out");
}

Console

true
false
It's sold out

Do not forget the brackets around the condition: !(seat == "available"). Here it gives the same result as seat != "available".

Practice

1Edit the programCurriculum practice

The prizes changed: target 8 also prints Video game Get, and target 7 also prints Candy Assortment Get. Add case 8: and case 7: by grouping them with the existing cases, without repeating console.log. With target = 7 it prints Candy Assortment Get.