Capacitative adding and subtracting is how many ADC (analog to digital converter) and DAC (digital to analog converter) chips work. There are many architectures, but capacitor arrays that are binary weighted are common, by switching them you can create or modify a voltage for a DAC, or use this to zero in/match this to the ADC input value. A common architecture that does this is called SAR ADC [0], which basically uses a DAC as part of the ADC, and it is often a capacitive DAC.

[0] https://en.m.wikipedia.org/wiki/Successive-approximation_ADC