The literal answer is supply and demand, the amount the stocks are assessed at is based solely on the current supply of shares on the market compared to the current demand.

The changes are made in the following factors means the stock value should be change

Interest rate of RBI and Federal bank,

Economic changes(inflation ,deflation etc)

Economic indicator,

Foreign exchange rate

The perceptions of those looking to buy or sell. Those perceptions can be based on anything, nothing, good information, bad information, no information, logic, emotion, whatever else you can think of.

Investors buying and selling

Buyers think the company is work more, or sellers think it's worth less.

In short, supply and demand - as always.