When you do:-
EEPROM.write(cData, sensorValue);
You only write one byte of data.
When you do:-
sensorValue = analogRead(analogInPin);
You create a variable that takes up 2 bytes of data. In order to write that value you need to split it up into two parts
EEPROM.write(cData, sensorValue & 0xff);
EEPROM.write(cData+1, sensorValue >> 8);
When you increment cData you need to do it by two because each value you put into EEPROM takes up two bytes.
// not cData++; but
cData+=2;
So you also need to do this when reading:-
value = EEPROM.read( addr ) + (EEPROM.read( addr+1 ) << 8);
and again increment by 2
// not cData++; but
cData+=2;
At the start of your loop() put
if(cData >= 20) cData = 0; // keeps the value under 10 values