File content as of revision 3:99acbebbed6c:

#include "mbed.h"

AnalogOut aout(p18);
AnalogIn ain(p15);
DigitalOut led1(LED1);
DigitalOut led2(LED2);
DigitalOut led3(LED3);
DigitalOut led4(LED4);

int main()
{
    // part 1
    const double pi = 3.141592653589793238462;
    const double amplitude = 1.0f;
    const double offset = 65535/2; // 0xFFFF/2
    double rads = 0.0;
    uint16_t sample = 0;
    
    while(1) {
        // analog out 
        
        for (int i = 0; i < 720; i++) {
            rads = (pi * i) / 180.0f;
            sample = (uint16_t)(amplitude * (offset * (cos(rads + pi))) + offset);
            aout.write_u16(sample);
        }
        
        
        // analog in
        led1 = (ain > 0.2f) ? 1 : 0;
        led2 = (ain > 0.4f) ? 1 : 0;
        led3 = (ain > 0.6f) ? 1 : 0;
        led4 = (ain > 0.8f) ? 1 : 0;
        wait(.01);
    }
    
    /* part 5
    // demo from https://docs.mbed.com/docs/mbed-os-api-reference/en/5.1/APIs/communication/network_sockets/
    
    printf("Example network-socket HTTP client\n");

    // Brings up the network interface
    eth.connect();
    const char *ip = eth.get_ip_address();
    const char *mac = eth.get_mac_address();
    printf("IP address is: %s\n", ip ? ip : "No IP");
    printf("MAC address is: %s\n", mac ? mac : "No MAC");

    // Open a socket on the network interface, and create a TCP connection to mbed.org
    socket.open(&eth);
    socket.connect("developer.mbed.org", 80);

    // Send a simple http request
    char sbuffer[] = "GET / HTTP/1.1\r\nHost: developer.mbed.org\r\n\r\n";
    int scount = socket.send(sbuffer, sizeof sbuffer);
    printf("sent %d [%.*s]\r\n", scount, strstr(sbuffer, "\r\n")-sbuffer, sbuffer);

    // Recieve a simple http response and print out the response line
    char rbuffer[64];
    int rcount = socket.recv(rbuffer, sizeof rbuffer);
    printf("recv %d [%.*s]\r\n", rcount, strstr(rbuffer, "\r\n")-rbuffer, rbuffer);

    // Close the socket to return its memory and bring down the network interface
    socket.close();
    eth.disconnect();

    printf("Done\n");
    */
}