[vissin]

Quite unfortunately, there are many engineers who don't understand what their respective engineering field is all about. So Vaibhav, it is good of you to ask such a basic question (a question that most electronics engineers will answer incorectly)

You've had some answers here and so I will try not to repeat anything unnecessarily in my reply.

We devide signals in many ways. Analog (periodic & non-periodic) and Digital being two of our concern in this discussion. The difference between these two is that while Analog is continuous, Digital is not so. Digital signals instead identifies a 'quantum' which is the smallest change in signal that can be recognized.

Analog voltage, for an instance can take any value eg 1V, 1.45V, 3.268V... etc. All these values are acceptable subject to what level of accuracy you desire. A digital signal, on the other hand, with a quantumm of 1V can only take such values as 1V, 2V, 3V...etc. A value like 1.5V is not legal. It will be taken as 1V (or 2V depending on logic).

The above is a generic understanding of Digital and Analog. There are many further classification in the two. When you speak of '1' and '0' you're talking of "Binary Logic Digital Signal". In this only two logic levels of the signal are accepted, '1' and '0' which may represent 'true' and 'false' or 'on' and 'off'.

What analog value of the actual signal is taken as '1' and what is taken as '0' depends on the logic standard that being used. The most popular one (historically) being TTL logic. A newer one would be CMOS logic. You may search about these on google and study them. Pay attention to noise margin and other such concepts.

To answer your following question:
' are these inputs analog or digital??
if they are analog then how do we give a digital input??'

All natural signals are analog in nature. Digital signals don't exist on it's own. When you say 5V you're naming an analog value. Understand also that this 5V is not an absolute value. It's a differential value (5V with respect to a certain potential level accepted to be 0V). What you accept as logic '1' and what as logic '0' will be clear to you when you read about TTL and CMOS logics.