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Why array index always starts with zero?
Because that's how the language is defined. In C, C++, and many other languages, array indecies start with zero. This is by convention, and it also reflects the fact that, in C and C++, array-index syntax can also be expressed in pointer-offset syntax. The pointer locates the first element of the array, and the offset indicates how many elements to skip. If a is an array name, then the expression a[n] is completely identical to the expression *(a+n), and vice versa.
How does one determine which high index lens is best for their prescription when every optician gives a different answer?
Normally you should try to stay in the type of lense you have worn before. Your eyes will have become accustomed to seeing through this particular material and changing the material will cause some initial distortion. Avoid polycarbonate lenses in high plus prescriptions. ---- The question above does not have a simple answer as there is no one single lens that is the "best". There are a number of different factors that need to be taken into account when deciding which lens is the most suitable. The first thing to say is that there are many different manufacturers out there, with different brand names for their products; however, broadly speaking there is little to choose between different brands. Firstly, as a rule of thumb, the higher your prescription - the higher the index that you need. A standard lens is considered to be 1.5 index. In the plastic materials the usual choices are 1.6 / 1.67 / 1.74. In glass 1.6 /1.7 / 1.8 / 1.9. While Glass lenses are available in higher indecies than the plastic, the glass lenses are usually considerable heavier and therefore less well appreciated by patients. Secondly, the reason a person will want a high index lens is to have a finished pair of spectacles that are thinner, lighter and more comfortable to wear. Your choice of spectacle frame will heavily influence the final finished job. Generally the smaller the frame the better the finished lenses will be [for both short and long sight]. An aspheric lens design will generally give a thinner and better cosmetic appearance and often better peripheral vision. This makes a bigger difference in a plus [long sight] prescription. An aspheric 1.6 index lens will finish better for a long sight prescription than a higher index 1.67 lens in a spheric design. All high index lenses need an anti-reflection coating to reduce unwanted reflections from the lens surface- most high index lenses come with the coating as standard, though some places supply the lenses without a coating to reduce the cost [not a good idea]. Speak to your optometrist or dispensing optician and have them explain their decision but my advice is to choose a small frame, with a plastic high index lens with an aspheric design including an antireflection coating. Exactly which index will depend on your prescription and how much you want to spend. The brand or product name is irrelevant!
