This method of searching an array by looking at each item in turn is called linear search . If nothing is known about the order of the items in the array, then there is really no better alternative algorithm. But if the elements in the array are known to be in increasing or decreasing order, then a much faster search algorithm can be used. An array in which the elements are in order is said to be sorted . Of course, it takes some work to sort an array, but if the array is to be searched many times, then the work done in sorting it can really pay off.
Binary search is a method for searching for a given item in a sorted array.
For example, suppose that you are looking for the number 42 in a sorted array of 1000 integers. Let's assume that the array is sorted into increasing order. Suppose you check item number 500 in the array, and find that item is 93. Since 42 is less than 93, and since the elements in the array are in increasing order, we can conclude that if 42 occurs in the array at all, then it must occur somewhere before location 500. All the locations numbered 500 or above contain values that are greater than or equal to 93.