switch...case
Wie auch if-Statements, erlaubt es auch switch case, dass abhängig von der Bedingung in verschiedenen Situationen unterschiedlicher Code ausgeführt wird. Im Detail vergleicht switch case die Variablenwerte mit denen in den case-Statements. Wenn ein passendes case-Statement gefunden wird, so wird der Code in diesem case-Statement ausgeführt.
Das break-Keywort beendet das switch case-Statement und wird üblicherweise am Ende jedes case-Statements verwendet. Wenn kein break-Keywort verwendet wird, führt switch case alle Statements aus, bis ein break-Keywort auftaucht oder das switch case zu Ende ist.
switch (var) {
case label1:
break;
case label2:
break;
default:
break;
}
var: Eine Variable, die mit den eizelnen Fällen verglichen werden sollen. Erlaubte Datentypen: int, char.
label1, label2: Konstanten. Erlaubte Datentypen: int, char.
void setup() {
Serial.begin(9600);
Serial.println("====== TEST START ======");
for (int i = 0; i < 5; i++) {
switch (i) {
case 0:
Serial.print("Inside case 0: i = ");
Serial.println(i);
break;
case 1:
Serial.print("Inside case 1: i = ");
Serial.println(i);
break;
case 2:
Serial.print("Inside case 2: i = ");
Serial.println(i);
break;
default:
Serial.print("Inside default: i = ");
Serial.println(i);
break;
}
}
Serial.println("====== TEST END ========");
}
void loop() {
}
Das ergebnis am seriellen monitor:
====== TEST START ======
Inside case 0: i = 0
Inside case 1: i = 1
Inside case 2: i = 2
Inside default: i = 3
Inside default: i = 4
====== TEST END ========
※ Anmerkungen und Warnungen:
if we does not use the break in a case, the next case will also be executed. The execution is stopped when it reaches a break. Let's comment or remove a break in the above example and see the result.
void setup() {
Serial.begin(9600);
Serial.println("====== TEST START ======");
for (int i = 0; i < 5; i++) {
switch (i) {
case 0:
Serial.print("Inside case 0: i = ");
Serial.println(i);
break;
case 1:
Serial.print("Inside case 1: i = ");
Serial.println(i);
case 2:
Serial.print("Inside case 2: i = ");
Serial.println(i);
break;
default:
Serial.print("Inside default: i = ");
Serial.println(i);
break;
}
}
Serial.println("====== TEST END ========");
}
void loop() {
}
Das ergebnis am seriellen monitor:
====== TEST START ======
Inside case 0: i = 0
Inside case 1: i = 1
Inside case 2: i = 1
Inside case 2: i = 2
Inside default: i = 3
Inside default: i = 4
====== TEST END ========
As you can see, when i = 1, the code run through case 1 and case 2.
If we miss a break in a case by accident, it results in the wrong operation of the code. Why the language does not force to use break instead of optional? Let's see two advanced usages to know the reason why.
Let's see the below example:
void setup() {
Serial.begin(9600);
for (int i = 0; i < 5; i++) {
switch (i) {
case 0:
Serial.println("HELLO!");
break;
case 1:
Serial.println("ARDUINO");
break;
case 2:
Serial.println("ARDUINO");
break;
case 3:
Serial.println("ARDUINO");
break;
default:
Serial.println("ArduinoGetStarted.com");
break;
}
}
}
void loop() {
}
Das ergebnis am seriellen monitor:
HELLO!
ARDUINO
ARDUINO
ARDUINO
ArduinoGetStarted.com
In the above code, you can see the case 1, 2 and 3 have the same code (do the same work). Let's remove all code in the case 1 and case 2:
void setup() {
Serial.begin(9600);
for (int i = 0; i < 5; i++) {
switch (i) {
case 0:
Serial.println("HELLO!");
break;
case 1:
case 2:
case 3:
Serial.println("ARDUINO");
break;
default:
Serial.println("ArduinoGetStarted.com");
break;
}
}
}
void loop() {
}
Das ergebnis am seriellen monitor:
HELLO!
ARDUINO
ARDUINO
ARDUINO
ArduinoGetStarted.com
As you can see, the results of both example codes are the same. But the second example code are shorter. Furthermore, if you get familiar to the second example code, you will realize that the second code is more readable. That is the benefit of not using the break;
Let's see the below example:
void setup() {
Serial.begin(9600);
for (int i = 0; i < 4; i++) {
switch (i) {
case 0:
Serial.println("Hello!");
break;
case 1:
Serial.print("Let's learn ");
Serial.println("Arduino");
break;
case 2:
Serial.println("Arduino");
break;
default:
Serial.println("via ArduinoGetStarted.com");
break;
}
}
}
void loop() {
}
Das ergebnis am seriellen monitor:
Hello!
Let's learn Arduino
Arduino
via ArduinoGetStarted.com
In the above code, you can see the case 1 and 2 have the same a line of code (Serial.println("Arduino")). Let's compare with the below code:
void setup() {
Serial.begin(9600);
for (int i = 0; i < 4; i++) {
switch (i) {
case 0:
Serial.println("Hello!");
break;
case 1:
Serial.print("Let's learn ");
case 2:
Serial.println("Arduino");
break;
default:
Serial.println("via ArduinoGetStarted.com");
break;
}
}
}
void loop() {
}
Das ergebnis am seriellen monitor:
Hello!
Let's learn Arduino
Arduino
via ArduinoGetStarted.com
As you can see, the results of both example codes are the same. However, the second example code are shorter. That is another benefit of not using the break;
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