I2c communication between Raspberry Pi Pico and Arduino Nano

#include <Wire.h>

const int I2C_ADD =0x50;

  
void setup() {
    Wire.begin();
    Serial.begin(9600);
  
    pinMode(LED_BUILTIN, OUTPUT);

    digitalWrite(LED_BUILTIN, HIGH);
    delay(1000);
    digitalWrite(LED_BUILTIN, LOW);
    delay(1000);
    digitalWrite(LED_BUILTIN, HIGH);
    delay(1000);
    digitalWrite(LED_BUILTIN, LOW);
    delay(1000);
    digitalWrite(LED_BUILTIN, HIGH);
    delay(1000);
    digitalWrite(LED_BUILTIN, LOW);
}
  
void loop() {
  
    delay(1000);      
    
    for(int i = 0;i<100;i++){
       Wire.beginTransmission(I2C_ADD );
       Wire.write('a' );
       Wire.endTransmission();
       
       delay(500);
       digitalWrite(LED_BUILTIN, HIGH);
       delay(500);
       digitalWrite(LED_BUILTIN, LOW);
    }
}

static int I2C_ADD = 0x50;

int main() {
 
    stdio_init_all();
    
    i2c_init(i2c_default,  100000); //100kHZ
    gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
    gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
    gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);
    bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C));

    i2c_set_slave_mode(i2c_default,true,I2C_ADD);
    

    uint8_t buffer[1];   

    while(1){
        
        int readResult = i2c_read_blocking(i2c_default, I2C_ADD, buffer, 1, false);
        
        i f(readResult>0){
            printf("Lenght= %d. Received: %d\n",readResult, buffer[0]);
        }
       
    }
}