I'm new in programming and I don't understand the error

code: [select]

#include <newping.h>
#include <afmotor.h>
 
#define trigger_pin  13
#define echo_pin     11
#define max_distance 200
af_dcmotor motor(2, motor12_64khz); // create motor #2, 64khz pwm

 
newping sonar(trigger_pin, echo_pin, max_distance);
 
void setup() {
  serial.begin(115200);
  serial.begin(9600);           // set serial library @ 9600 bps
  serial.println("motor test!");
 
  motor.setspeed(255);     // set speed 200/255
}
 
void loop() {
  delay(50);
  unsigned int distanceincms = sonar.ping() / us_roundtrip_cm; // send ping, ping time in microseconds (us) , convert centimeters (cm)
  serial.println("distance: " + string(distanceincms) + "cm");
 
  if(distanceincms < 50) {
    motor.run(forward);
  } else {
    motor.run(release);
  }
}

could explain me error? want make dc motor move when distance less 50cm.

please give details of problem you're experiencing.

is error when compile sketch?

is error when upload sketch?

or code compiling , uploading correctly not working expect?

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