Many choices with switch · Lessons

One value, many cases

When you compare one value against many possibilities, switch is tidier than a long chain of else if. Each case gives a value; xTalk runs the lines of the first one that matches, until a break. default runs when nothing matched.

ExampleRun it in the playground

put "Save" into tChoice
switch tChoice
   case "Open"
      put "Opening a file"
      break
   case "Save"
      put "Saving your work"
      break
   default
      put "Not a menu item:" && tChoice
end switch

Output

Saving your work

Several values, one answer

Cases with no lines between them share the lines that follow. Matching text ignores capitals, as every text comparison does.

ExampleRun it in the playground

put "SUN" into tDay
switch tDay
   case "Sat"
   case "Sun"
      put "Weekend"
      break
   default
      put "Weekday"
end switch

Output

Weekend

Do not forget break

Without break, xTalk carries on into the next case's lines, whether it matches or not. Occasionally that is what you want; usually it is a bug.

ExampleRun it in the playground

put 2 into tLevel
switch tLevel
   case 1
      put "Easy"
   case 2
      put "Medium" -- no break here...
   case 3
      put "Hard"   -- ...so this runs too
      break
   default
      put "Unknown level"
end switch

Output

Medium
Hard

Cases that are conditions

A switch with nothing after it takes a condition in each case, and runs the first that is true. It reads well for ranges.

ExampleRun it in the playground

put 37 into tCelsius
switch
   case tCelsius < 0
      put "Freezing"
      break
   case tCelsius < 20
      put "Mild"
      break
   case tCelsius < 35
      put "Warm"
      break
   default
      put "Hot"
end switch

Output

Hot

Try it yourself

Write a switch that turns a month's number (1 to 12) into its season in the northern hemisphere: 12, 1 and 2 are winter, 3 to 5 spring, 6 to 8 summer, and 9 to 11 autumn. Try it with month 4.

Show a solution

ExampleRun it in the playground

put 4 into tMonth
switch tMonth
   case 12
   case 1
   case 2
      put "Winter"
      break
   case 3
   case 4
   case 5
      put "Spring"
      break
   case 6
   case 7
   case 8
      put "Summer"
      break
   default
      put "Autumn"
end switch

Output

Spring

Words in this lesson

switchcasebreakdefaultend switch

Each one finds every lesson that uses it. The Dictionary has the whole story of each, with its syntax and more examples.