void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");
}

void toUpperCase(char *str) {
  // Loop through each character in the string
  for (int i = 0; str[i] != '\0'; i++) {
    // If the character is lowercase, convert it to uppercase
    if (str[i] >= 'a' && str[i] <= 'z') {
      str[i] = str[i] - 32;
    }
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  // Declare and initialize the character array with a null terminator
  char greeting[] = "Hello, world!\0";
  
  // Call the function to convert greeting to uppercase
  toUpperCase(greeting);

  // Print the modified greeting to the Serial monitor
  Serial.println(greeting);
  
  // Wait for a second before repeating the loop
  delay(1000);
}