File content as of revision 0:31a72c321609:

#include "mbed.h"
#include "hcsr04.h"

//I2C to_main(dp4,dp5);
//I2CSlave to_main(dp4,dp5);
Serial to_main(dp4,dp5);
//Serial pc(USBTX,USBRX);

HCSR04 front(dp24,dp25);
HCSR04 back(dp22,dp23);
HCSR04 right(dp20,dp21);
HCSR04 left(dp18,dp19);

//DigitalOut led(dp12);

//const int addr=0x0A;

int main() {
    char dist[4]={0};
    //to_main.baud(19200);
    //to_main.address(addr);
    while(1) {
        front.start();
        back.start();
        right.start();
        left.start();
        dist[0]=front.get_dist_cm();
        dist[1]=back.get_dist_cm();
        dist[2]=right.get_dist_cm();
        dist[3]=left.get_dist_cm();
        //led=to_main.write(addr,dist,4);
        //led=to_main.write(dist, 4);
        to_main.putc(1);
        for(int i=0;i<4;i++){
            to_main.putc(dist[i]);
        }
        //pc.putc('\n');
    }
}