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    <p>Welcome to <a href="http://www.idryman.org/blog/2012/11/21/integer-promotion/" rel="noreferrer">integer promotion</a>. If I may quote from the website:</p> <blockquote> <p>If an int can represent all values of the original type, the value is converted to an int; otherwise, it is converted to an unsigned int. These are called the integer promotions. All other types are unchanged by the integer promotions.</p> </blockquote> <p>C can be really confusing when you do comparisons such as these, I recently puzzled some of my non-C programming friends with the following tease:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;string.h&gt; int main() { char* string = "One looooooooooong string"; printf("%d\n", strlen(string)); if (strlen(string) &lt; -1) printf("This cannot be happening :("); return 0; } </code></pre> <p>Which indeed does print <code>This cannot be happening :(</code> and seemingly demonstrates that 25 is smaller than -1! </p> <p>What happens underneath however is that -1 is represented as an unsigned integer which due to the underlying bits representation is equal to 4294967295 on a 32 bit system. And naturally 25 is smaller than 4294967295.</p> <p>If we however explicitly cast the <code>size_t</code> type returned by <code>strlen</code> as a signed integer:</p> <pre><code>if ((int)(strlen(string)) &lt; -1) </code></pre> <p>Then it will compare 25 against -1 and all will be well with the world.</p> <p>A good compiler should warn you about the comparison between an unsigned and signed integer and yet it is still so easy to miss (especially if you don't enable warnings).</p> <p>This is especially confusing for Java programmers as all primitive types there are signed. Here's what James Gosling (one of the creators of Java) <a href="http://www.gotw.ca/publications/c_family_interview.htm" rel="noreferrer">had to say on the subject</a>:</p> <blockquote> <p>Gosling: For me as a language designer, which I don't really count myself as these days, what "simple" really ended up meaning was could I expect J. Random Developer to hold the spec in his head. That definition says that, for instance, Java isn't -- and in fact a lot of these languages end up with a lot of corner cases, things that nobody really understands. Quiz any C developer about unsigned, and pretty soon you discover that almost no C developers actually understand what goes on with unsigned, what unsigned arithmetic is. Things like that made C complex. The language part of Java is, I think, pretty simple. The libraries you have to look up.</p> </blockquote>
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