What is the minimum number of times you must press the C button on a calculator?

The minimum number of times you need to press the C button on a calculator depends on the context of its usage. If the goal is to clear any existing input or calculation, you would need to press the C button once. Pressing it once will usually reset the calculator to its default state, clearing any numbers or operations entered previously. If your intention is something different, such as clearing multiple calculations in different instances, then the minimum number of presses could increase, dependent on how many distinct instances you need to clear.