LEGO MINDSTORMS Robots Manual page 178

if (SENSOR_1 < 0xf000) {
// Touch sensor is pressed.
}
If you're working with light or rotation sensors, legOS does offer some help. First, you can set inputs to be active or passive:
void ds_active(unsigned∗ const sensor)
void ds_passive(unsigned∗ const sensor)
Use these functions to set the specified sensor to active or passive mode. The light and rotation sensors are active sensors; the touch and temperature sensors are passive.
The argument to these functions is the address of one of the sensor values. For example, to set input 2 to be active, you would do this:
ds_active(&SENSOR_2);
Processed light sensor values can be retrieved with the following macros:
LIGHT_1
LIGHT_2
LIGHT_3
These macros process raw input values to produce a light sensor reading in the range from 0 to approximately LIGHT_MAX.
legOS also supports rotation sensors with the following functions:
void ds_rotation_on(unsigned∗ const sensor)
void ds_rotation_off(unsigned∗ const sensor)
These functions turn on or off rotation counting for the specified input.
void ds_rotation_set(unsigned∗ const sensor, int pos)
This function sets the current rotation count of the given input.
Once you get the input set up for rotation, you can retrieve the rotation value with one of the following macros:
ROTATION_1
ROTATION_2
ROTATION_3
These macros return the rotation count for each of the inputs.
Setting up input 3 for a rotation sensor, then, looks something like this:
ds_active(&SENSOR_3);
ds_rotation_on(&SENSOR_3);
ds_rotation_set(&SENSOR_3, 0);
To actually read the rotation value, you would just use the ROTATION_3 macro.
Page 197