how to write code for the input constraints of about 10^9 etc.that much size cannot be initialise by array.than how to do it.?

There won’t be any problem on CodeChef with total number of inputs about 10^9 however each element of the input can be of the order of 10^9 or even more. At max total number of inputs will always be of the order of 10^7. This much size global arrays are possible in all programming languages. If by chance you get some problem then there would always be some formula or concept where you won’t have to read all the inputs at all.

@macin40 : You basically need an algorithm which does not require a data structure to store all such values . For eg. if i ask you to calculate number of even numbers from 1 to N . Input consists of a number , N . Constraints are 1 <= N <= 10^9 . In this case you can simply output N/2 , no storage needed at all .