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copied!<ul> <li>Money (salary): <code>Decimal</code>.</li> <li>Birthday: <code>DateTime</code>.</li> <li>Name: <code>String</code>.</li> <li>Social Security Number: <code>String</code>.</li> <li>Weight of the earth: <code>float</code> or <code>double</code>.</li> </ul> <h1>Explanation</h1> <h2>Money</h2> <blockquote> <p>The Decimal value type is appropriate for financial calculations requiring large numbers of significant integral and fractional digits and no round-off errors. The Decimal type does not eliminate the need for rounding. Rather, it minimizes errors due to rounding. <a href="http://msdn.microsoft.com/en-us/library/system.decimal.aspx" rel="nofollow noreferrer">- MSDN</a></p> </blockquote> <p>It also can't be an integer because you'll need a decimal point ($59.9) and integers cannot have one, you'd have to convert it, e.g. with a cast which will always round it up for you: <code>((int)7.001) == 8</code> is <code>true</code>.</p> <p>You won't use a string either. Text is just the wrong representation (quantifying money does not result in a list of characters, right?). And you'd also like to run some math, I'm sure, and you cannot do that with strings directly because it's not numeric. E.g. <code>2 + 2 = 4</code>. Try the same with strings: <code>"2" + "2" = "22"</code> (<code>+</code> is overloaded: it adds for numerics and concatenates for strings).</p> <p><strong>Edit: My opinion of this has changed!</strong>.</p> <p>Computers and floating points are notoriously complicated and even error-prone (if you do not know precisely what you're doing). I suggest to not use them for money or anything precise & critical. </p> <p>I recommend to use an integer type that will not overflow (for arbitrary size use <code>BigInteger</code>) and use it to represent the lowest resolution you need. E.g. you're likely to be okay with representing dollars as cents, so <code>150</code> is how you would represent <code>1.5</code>. Away with rounding errors and scary IEEE standards! woohoo! plus computers are faster with integers so you would typically get better performance, especially if you can manage to use an <code>int</code>, i.e. you're <em>certain</em> it will not overflow.</p> <h2>Phone Numbers & Security Number</h2> <p>Phone numbers and security numbers are called numbers, but really they're just a string of digits, aren't they? at least that seems the common perception. Well that already tells you: use a string.<br /> You're also unlikely to use a phone number for mathematical operations? (although I do suppose summing up phone numbers would make one wild afternoon).</p> <h2>Birthday</h2> <p><code>DateTime</code> is the standard .NET type for dates, I'm sure there's no need to explain why, the name is self-explanatory.</p> <h2>Name</h2> <p>String for obvious reasons.</p> <h2>Weight</h2> <p><code>double</code> or <code>float</code> are used to this kind of things. It depends on how much precision you want. Double gives you more, but the trade-off is that it takes more memory. It only makes a real difference when you have tons of them. My rule of thumb is to go with doubles unless I actually need to use a single/float. That being said, from my experience, almost every game that has something like that (a gravity force value, a weight, and such) is usually a <code>float</code> and rarely a <code>double</code>. Sometimes the domain will give you a different rule of thumb while you're working in it.</p> <p>Differences between float & double: <a href="https://stackoverflow.com/questions/2386772/difference-between-float-and-double">link</a> & another <a href="https://stackoverflow.com/questions/1074474/should-i-use-double-or-float">link</a>.</p>

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