{"id":3593,"date":"2011-01-11T16:00:00","date_gmt":"2011-01-11T16:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vcblog\/2011\/01\/11\/c-programming-interviews-what-interviewers-want-you-to-show\/"},"modified":"2021-10-06T11:00:30","modified_gmt":"2021-10-06T11:00:30","slug":"c-programming-interviews-what-interviewers-want-you-to-show","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/c-programming-interviews-what-interviewers-want-you-to-show\/","title":{"rendered":"C++ Programming Interviews: What Interviewers Want You To Show"},"content":{"rendered":"

A recent study<\/a> showed that C++ is still among the most used languages (ahead of any other Visual Studio officially supported language like C# or Visual Basic). But despite being widely used and known by several generations of developers \u2013thanks that it has been out there for decades now, while being still the most taught language in the Academy- when you look for a C++ development job those facts don\u2019t guarantee that you\u2019ll be chosen. It will depend on how well you perform in the programming interview \u2013among other factors. Regardless of how deeply you know the C++ syntax, how many STL components you memorize, it will be your abilities of using \u201cthe right tool for the right task\u201d what will define your eligibility. This post will seem like a lost chapter of the book Programming Interviews Exposed-Secrets to Landing Your Next Job, 2nd Edition<\/a> [Mongan, Soujanen, Gigu\u00e8re; Wrox 2007], but it\u2019s based on reflections I can share from a programming interview I participated. While this post is initially intended for candidates who are to be interviewed, it feels like a novice programming interviewer may get some ideas from here about what to check on a candidate.<\/p>\n

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In an interview, I was asked to pseudo-code a function that returns the decimal equivalent of a roman numeral received as input. It seems like a trivial challenge but what the aspiring candidate must keep in mind, first of all, is the fact that the interviewer isn\u2019t curious about your background with roman numerals. What he\/she wants to check are your abilities in problem solving. Beside, the roman numeric system isn\u2019t that trivial compared with the decimal system. It\u2019s non-positional (in the sense that you don\u2019t get ones in the last position, tens in the penultimate, hundreds in the position before, etc.). Beside, the system only contains symbols to represent powers of 10 (10n<\/sup>, n=0, \u2026,3)<\/em> and 5×10n<\/sup> (n=0, \u2026,2)<\/em>. Bizarre enough, huh? I wonder if the romans created this numeral system in order to later use it in programming interviews.<\/p>\n

Regarding those unusual features, the first thing I started doing \u2013in front of my interviewer and with the whiteboard marker in my hand- was an exploration of typical equivalences, easy and not so easy roman numeral cases with their expected result. Those served me to both, craft the algorithm toward the general case and test my derived solution for correctness.<\/p>\n

\"Image<\/a><\/p>\n

Those and some few other examples help us determine some basic syntax rules in roman numerals. Rules like repetition of characters (III, CC, XXX, \u2026); subtraction (IX, CD, \u2026); etc.<\/p>\n

Those same rules have their own limitations, for instance<\/p>\n

\"Image<\/a><\/p>\n

In other words, repetition is only allowed to characters I, X, C and M (1, 10, 100 and 1000 respectively) but not to V, L, D (5, 50, 500 respectively) and -while not represented in these examples- it can\u2019t happen more than three times either. Subtracting V, L or D isn\u2019t allowed either. Likewise, the 3rd erroneous example shows that we can get a character subtracting its immediate follower, but this latter can\u2019t subtract to a third one (that is to say, a subtracting portion in a whole roman numeral only involves two characters).<\/p>\n

Talk about all these rules, exceptions and thoughts like thinking in loud voice, as you write them down in some margin (whiteboard in my case but it could be a piece of paper you were given). If available, use two different colors to separate DO\u2019s and DON\u2019T\u2019s.<\/p>\n

\"Image<\/a><\/p>\n

There are yet other syntax rules but, with my interviewer, we agreed to stop here as was good enough to show some skills in the remaining time.<\/p>\n

Let\u2019s start shaping the function skeleton, its public interface and expected return types<\/p>\n

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  1. namespace<\/span> RomanNumeral {<\/li>\n
  2. \u00a0\u00a0\u00a0\u00a0unsigned<\/span> int<\/span> rtoi(const<\/span> basic_string<Ch>& romanStr);<\/li>\n
  3. \u00a0\u00a0\u00a0\u00a0…<\/li>\n
  4. }<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n

    The function name, rtoi()<\/span>, was chosen for its similarity in intention with atoi()<\/span>. There are several decisions to explain here:<\/p>\n