#include <OneWire.h>
OneWire ds_1(10); //sensor 1 on pin 10
OneWire ds_2(11); //sensor 2 on pin 11
OneWire ds_3(12); //sensor 3 on pin 12
//Then search every pin for its address and request temps
DallasTemperature sensor_1(&ds_1);
DallasTemperature sensor_2(&ds_2);
DallasTemperature sensor_3(&ds_3);
........
sensor_1.begin();
sensor_1.requestTemperatures();
temp_1 = sensor_1.getTempCByIndex(0);
(3 times) you get the idea