Leer switch-case Statement in Dart | Conditional Statements

When there are many conditions to check, using multiple if-else statements can become inconvenient.

In this example, the code checks the value of the dayOfWeek variable and prints a message for the matching day. If it’s one of the weekdays, it prints the day’s name; otherwise, it prints "Weekend".

main.dart


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void main() {
  String dayOfWeek = "Friday";

  if (dayOfWeek == "Monday")
  {
    print("Today is Monday.");
  }
  else if (dayOfWeek == "Tuesday")
  {
    print("Today is Tuesday.");
  }
  else if (dayOfWeek == "Wednesday")
  {
    print("Today is Wednesday.");
  }
  else if (dayOfWeek == "Thursday")
  {
    print("Today is Thursday.");
  }
  else if (dayOfWeek == "Friday")
  {
    print("Today is Friday.");
  }
  else
  {
    print("Weekend");
  }
}

The code may look confusing, but it can be made more readable using a switch-case statement. A switch-case statement includes several parts: the switch keyword, multiple case options to compare values, and an optional default block that runs if no case matches.

main.dart


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switch(expresion) {
  case value_1: 
  // code to be executed
  case value_2: 
  // code to be executed
  .............
  default: // code to be executed if all cases are not matched
}

switch(expression): evaluates the value of expression;
case value_1: if expression equals value_1, the corresponding code runs;
default: executes if none of the case values match.

A switch-case statement is a construct that allows you to execute a block of code based on the value of a variable. The variable is called the switch variable. The switch variable is evaluated once, and the corresponding block of code is executed.

main.dart


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void main() {
  String dayOfWeek = "Monday";

  switch (dayOfWeek) {
    case "Monday":
      print("Today is Monday.");
      
    case "Tuesday":
      print("Today is Tuesday.");
      
    case "Wednesday":
      print("Today is Wednesday.");
      
    case "Thursday":
      print("Today is Thursday.");
      
    case "Friday":
      print("Today is Friday.");
      
    default:
      print("Weekend");
  }
}

In this example, the switch variable is dayOfWeek. It’s evaluated once, and the matching code block runs.
Once a matching case executes, the remaining cases are skipped.
If dayOfWeek doesn’t match any case, the default block runs, in this case, it prints "Weekend".

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When there are many conditions to check, using multiple if-else statements can become inconvenient.

main.dart


              12345678910111213141516171819202122232425262728
            
void main() {
  String dayOfWeek = "Friday";

  if (dayOfWeek == "Monday")
  {
    print("Today is Monday.");
  }
  else if (dayOfWeek == "Tuesday")
  {
    print("Today is Tuesday.");
  }
  else if (dayOfWeek == "Wednesday")
  {
    print("Today is Wednesday.");
  }
  else if (dayOfWeek == "Thursday")
  {
    print("Today is Thursday.");
  }
  else if (dayOfWeek == "Friday")
  {
    print("Today is Friday.");
  }
  else
  {
    print("Weekend");
  }
}

main.dart


              12345678
            
switch(expresion) {
  case value_1: 
  // code to be executed
  case value_2: 
  // code to be executed
  .............
  default: // code to be executed if all cases are not matched
}

switch(expression): evaluates the value of expression;
case value_1: if expression equals value_1, the corresponding code runs;
default: executes if none of the case values match.

main.dart


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void main() {
  String dayOfWeek = "Monday";

  switch (dayOfWeek) {
    case "Monday":
      print("Today is Monday.");
      
    case "Tuesday":
      print("Today is Tuesday.");
      
    case "Wednesday":
      print("Today is Wednesday.");
      
    case "Thursday":
      print("Today is Thursday.");
      
    case "Friday":
      print("Today is Friday.");
      
    default:
      print("Weekend");
  }
}

In this example, the switch variable is dayOfWeek. It’s evaluated once, and the matching code block runs.
Once a matching case executes, the remaining cases are skipped.
If dayOfWeek doesn’t match any case, the default block runs, in this case, it prints "Weekend".

Was alles duidelijk?

Bedankt voor je feedback!

Sectie 3. Hoofdstuk 4