I have a doubt how a coin value is decided before ICO or release?
The basic formula is the market supply versus how much the market demand is and willing to pay. These two things determine us a marketcap and that is how the value is determined through these basic principles.
The OP is asking on how the price is defined of a coin before the ICO and not afterwards . MarketCap and supply / demand factors are only for the coins which are listed on the exchnage. For the ICO ones, the dev himself set the price depending upon the coin supply and the projects which he has in his mind to promote the coin.
Too high a pirce at ICO will give very little investment and too low a price will make the coin useless. The price should be carefully determine in ICO so that if can retain its value after the ICO as well.