Switch / Enum Part 2 (Switch)

switch Statements in C++

Consider

We are trying to design a self-driving car, and it has a finite set of actions (these are simplified):

• turn right
• turn left
• continue straight
• arrive

Consider

To give instructions to the user, we need conditional logic

int action = ...; 	
if (action == 1) {			//turn right
    Serial.println("Turn right (you can turn on red)");
} else if (action == 2)  { 	//turn left
    Serial.println("Turn left (wait for arrow)");
} else if (action == 3)  { 	//continue
    Serial.println("Keep going straight");
} else if (action == 4)  { 	//arrived
    Serial.println("You have arrived!");
}
else {
    Serial.println("Error!")
}

Consider

• Using if this way is a perfectly fine way to handle conditional logic
• However, for a finite set of options, there is an easier way
• switch statements provide a way to choose between specific, finite values

switch Statement Syntax

switch (<<variable>>) {
    case <<FIRST_VALUE>>:
        # do some code if variable == VALUE_1
    break;
    case <<SECOND_VALUE>>:
        # do some code if variable == VALUE_2
    break;
    default:
        # do some code if variable is anything else 
}

switchStatement Syntax

switch (<<variable>>)

• variable can be an int (or short, byte, char)
• variable can not be a string

switch Statement Syntax

switch (<<variable>>) {
    case <<FIRST_VALUE>>:
        # do some code if variable == FIRST_VALUE
    break;

• switch will attempt to match variable to the value specified by each case label (e.g. VALUE_3)
• When a match is found, the code is executed
• This is the equivalent of if ... else if
• break; is required after executing the code for that case

switch Statement Syntax

switch (<<variable>>) {
	# ...
    default:
    # do some code if variable is anything else 

• default will execute if none of the cases match variable
• This is the equivalent of else

Partially Code: switchcompared to if

if (action == 0) {			//turn right
    Serial.println("Turn right");
} else if (action == 1)  { 	        //turn left
    Serial.println("Turn left");     //...more else if...
else {
    Serial.println("Error!")
}

switch (action) {			
    case 0:					//turn right
    	Serial.println("Turn right (you can turn on red)");
    break;      //...more cases...
    default:
	    Serial.println("Error!");
}

Full switch Example

int action = ...; 	
switch (action) {			
    case 0:					//turn right
    	Serial.println("Turn right (you can turn on red)");
    break; 
    case 1:					//turn left
    	Serial.println("Turn left (wait for arrow)");
    break;
    case 2:	 				//continue
    	Serial.println("Keep going straight");
    break;
    case 3:	 				//arrived
    	Serial.println("You have arrived!");
    break;
    default:
	    Serial.println("Error!");
}

Summary

• switch provides a simplified structure to decided between a small number fixed values (int typically)
• switch does not work with string