I check the libraries you are using from: GitHub - sparkfun/SparkFun_ADC_Block_for_Edison_CPP_Library: C++ library and example for using SparkFun's ADC block for …
These libraries use the MRAA library so I would like to know if you have the latest version on your board or which version do you have.
You can install the latest version by running the following commands:
echo "src iotkit http://iotdk.intel.com/repos/3.0/intelgalactic/opkg/i586" > /etc/opkg/iotkit.conf
opkg install mraa
I suggest you to also install the UPM library too (just in case), you can check some examples of this libray in:upm/examples at master · intel-iot-devkit/upm · GitHub. If you are using one of those sensors, the library will help you a lot.
opkg install upm
Also, check the raw readings from the ADC in /sys/bus/iio/devices/iio:device1, if you are using the AN0 you should be able to see the readings with cat /sys/bus/iio/devices/iio:device1/in_voltage0_raw. Start checking these files while using the sensors so you can see if the ADC is working or not, then you can start debugging the code and libraries.