Convert string to lowercase or uppercase in Arduino

In order to convert a string to lower/upper case, the in-built .toLowerCase() and .toUpperCase() functions can be used.

Note: These functions change the original string itself, and don't return a new string with the changes.

The implementation is shown below −

Example

void setup() {
   Serial.begin(9600);
   Serial.println();
   String s1 = "Hello World";
   Serial.println(s1);
   s1.toLowerCase();
   Serial.println(s1);
   s1.toUpperCase();
   Serial.println(s1);
}
void loop() {
   // put your main code here, to run repeatedly:
}

The corresponding Serial Monitor output is −

Output

As you can see, the changes have been made in s1 itself. The return of .toUpperCase() and .toLowerCase() is void.