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copied!<p>You are a lucky lucky man. This won't solve the general problem of <code>long double</code> on MinGW, but I'll explain what is happening to your problem. Now, in a far far day when you'll be able to upvote, I want your upvote. :-) (but I don't want this to be marked as the correct response. It's the response to what you need, but not to what you asked (the general problem in your title <code>scanf not taking in long double</code>) ).</p> <p>First, the solution: use <code>float</code>. Use <code>%f</code> in <code>scanf</code>/<code>printf</code>. The results comes perfectly equal to the ones given as the solution in your site. As a sidenote, if you want to <code>printf</code> with some decimals, do as it's showed in the last printf: <code>%.10f</code> will print 10 decimals after the decimal separator.</p> <p>Second: why you had a problem with <code>double</code>s: the <code>res=sqrt()</code> calculates a square root. Using <code>float</code>s, <code>l*l+r*r-2*cosa*l*r</code> == 0.0, using <code>double</code>s it's -1.0781242565371940e-010, so something near zero BUT NEGATIVE!!! So the <code>sqrt(-something)</code> is <code>NaN</code> (Not a Number) a special value of <code>double/float</code>. You can check if a number is <code>NaN</code> by doing <code>res != res</code>. This because <code>NaN != NaN</code> (but note that this isn't guaranteed by older C standards, but in many compilers on Intel platform do it. <a href="http://www.gnu.org/s/hello/manual/libc/Infinity-and-NaN.html" rel="nofollow">http://www.gnu.org/s/hello/manual/libc/Infinity-and-NaN.html</a>). And this explains why the <code>printf</code> printed something like <code>-1.#IO</code>.</p>

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