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    <p>A look-up table <em>might</em> be faster:</p> <pre><code>char isvowel[UCHAR_MAX+1] = { 0 }; // or int instead of char, try both isvowel['a'] = 1; isvowel['e'] = 1; isvowel['i'] = 1; isvowel['o'] = 1; isvowel['u'] = 1; isvowel['A'] = 1; isvowel['E'] = 1; isvowel['I'] = 1; isvowel['O'] = 1; isvowel['U'] = 1; ... if (isvowel[(unsigned)name[i]]) vow_cnt++; </code></pre> <p>You could also try letting the compiler decide how to optimize, by using a switch:</p> <pre><code>switch(name[i]) { case 'a': case 'e': case 'i': case 'o': case 'u': case 'A': case 'E': case 'I': case 'O': case 'U': ++vow_cnt; default: } </code></pre> <p>Then again, either or both might be slower. You'd have to test it with more realistic data, since "optimizing" a program that only processes one short string is pretty futile. It will be effectively instantaneous whatever you do, so don't waste your own time. Performance only matters if you're processing a lot of data, so either one enormous string or lots of strings.</p> <p>ASCII has a trick, that <code>name[i]</code> is a particular letter (either case) if and only if <code>name[i] | 0x20</code> is that letter (lower case). You can use that to halve the number of case labels or (with care) the size of the lookup table. That may or may not affect performance.</p> <p>If you want to try a completely different approach, see how it performs, you can take the complicated logic and branching out of the loop:</p> <pre><code>size_t charcounts[UCHAR_MAX+1] = { 0 }; char *p = name; while (*p) { ++charcounts[(unsigned)*p]; ++p; } vow_cnt = charcounts['a'] + charcounts['e'] + ... + charcounts['U']; </code></pre> <p>This is likely to be slower for short strings, since the <code>charcounts</code> array has to be cleared for each string you test. It has a chance for large amounts of data, though.</p>
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    1. POCount no of vowels in a string
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    1. USSteve Jessop
    1. USSteve Jessop
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    1. COWhat about using `tolower` or `toupper` to remove half the cases?
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      1. USThomas Matthews
    2. CO@Thomas: yes, that's the clear, sensible, maintainable way to write it. But if you can assume ASCII then the `0x20` trick is potentially faster because it cuts a corner. For example it transforms `[` to `{`, which we don't care about just for this purpose but `tolower` has to avoid.
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      1. USSteve Jessop
    3. CO+1, but vow_count+=isvowel[(unsigned)name[i]] will be fastest. Both faster than the if, and slightly faster than switch/case (jumps).
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      1. USRon Maimon
 

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