Hi, Uthpala Hathnagoda Welcome to JR.
You can achieve this in many ways- by using for loop (you may be done this in other languages like c,c++). Or there is one method in an Array name as sort(int[] arr). Using this method you can Sorts the array of into ascending numerical order. Once you get sorted array it is easy to find out max and min element in that array.

Life is easy because we write the source code.....

I think the idea is to find the maximum value without sorting. this is a common homework task for beginners. Please, Uthpala Hathnagoda, show us what you have got so far.

If you have got nowhere, get a pencil and paper and a large eraser. The eraser is by far the most useful piece of hardware . Write out an unsorted array of numbers. Write a maximum variable, give it an initial value, and write down how you think you can iterate through the array and get maximum to be equal to the largest value. Leave spaces after each line . . .

. . . then go back and enhance your algorithm by adding a minimum value.

The following sentences show what you are aiming for: all words of one syllable.
Once you have made that work well and work right, write down what you have done in small words. Then you can change what you wrote into code.