Is else if faster than switch case

Question

I m an ex Pascal guy  currently learning C   My question is the following   Is the code below faster than making a switch   int a   5   if  a    1               else if a    2               else if a    3               else if a    4               else            And the switch   int a   5   switch a        case 1                      break       case 2                      break       case 3                      break       case 4                      break       default                      break        Which one is faster   I m asking  because my program has a similar structure  many  many  else if  statements   Should I turn them into switches

User · Accepted Answer

For just a few items  the difference is small  If you have many items you should definitely use a switch   If a switch contains more than five items  it s implemented using a lookup table or a hash list  This means that all items get the same access time  compared to a list of if s where the last item takes much more time to reach as it has to evaluate every previous condition first

User · Answer

Another thing to consider  is this really the bottleneck of your application  There are extremely rare cases when optimization of this sort is really required  Most of the time you can get way better speedups by rethinking your algorithms and data structures

User · Answer

Far more important than the performance benefits of switch  which are relatively slight  but worth noting  are the readability issues   I for one find a switch statement extremely clear in intent and pure whitespace  compared to chains of ifs

User · Answer

I d say the switch is the way to go  it is both faster and better practise   There are various links such as  http   www blackwasp co uk SpeedTestIfElseSwitch aspx  that show benchmark tests comparing the two

User · Answer

Technically  they produce the exact same result so they should be optimizable in pretty much the same way   However  there are more chances that the compiler will optimize the switch case with a jump table than the ifs   I m talking about the general case here   For 5 entries  the average number of tests performed for the ifs should be less than 2 5  assuming you order the conditions by frequency   Hardly a bottleneck to write home about unless in a very tight loop

User · Answer

Switch is generally faster than a long list of ifs because the compiler can generate a jump table  The longer the list  the better a switch statement is over a series of if statements

User · Answer

Shouldn t be hard to test  create a function that switches or ifelse s between 5 numbers  throw a rand 1 5  into that function and loop that a few times while timing it

User · Answer

Short answer  Switch statement is quicker  The if statement you need two comparisons  when running your example code  on average to get to the correct clause     The switch statement the average number of comparisons will be one regardless of how many different cases you have  The compiler VM will have made a  lookup table  of possible options at compile time    Can virtual machines optimize the if statement in a similar way if you run this code often

User · Answer

switch usually gets translated into a lookup table by the compiler  if possible  So lookup of an arbitrary case is O 1   instead of actually doing a few case comparisons before finding the one you want   So in many cases an if else if chain will be slower  Depending on the frequency with which your cases are being hit that may make no difference  though

User · Answer

Why do you care   99 99  of the time  you shouldn t care   These sorts of micro-optimizations are unlikely to affect the performance of your code   Also  if you NEEDED to care  then you should be doing performance profiling on your code  In which case finding out the performance difference between a switch case and an if-else block would be trivial   Edit  For clarity s sake  implement whichever design is clearer and more maintainable  Generally when faced with a huge switch-case or if-else block the solution is to use polymorphism  Find the behavior that s changing and encapsulate it  I ve had to deal with huge  ugly switch case code like this before and generally it s not that difficult to simplify  But oh so satisfying

User · Answer

I m not sure  but i believe the speed of one or the other changes depending on the programming language you re using   I usually prefer to use switch  That way the code is simplear to read

User · Answer

see  http   msdn microsoft com en-us library system reflection emit opcodes switch 28VS 71 29 aspx  switch statement basically a look up table it have options which are known and if statement is like boolean  type  according to me switch and if-else are same but for logic switch can help more better  while if-else helps to understand in reading also

User · Answer

Believing this performance evaluation  the switch case is faster   This is the conclusion      The results show that the switch statement is faster to execute than the if-else-if ladder  This is due to the compiler s ability to optimise the switch statement  In the case of the if-else-if ladder  the code must process each if statement in the order determined by the programmer  However  because each case within a switch statement does not rely on earlier cases  the compiler is able to re-order the testing in such a way as to provide the fastest execution

User · Answer

Since the switch statement expresses the same intent as your if   else chain but in a more restricted  formal manner  your first guess should be that the compiler will be able to optimize it better  since it can draw more conclusions about the conditions placed on your code  i e  only one state can possibly be true  the value being compared is a primitive type  etc    This is a pretty safe general truth when you are comparing two similar language structures for runtime performance

[c#] Is "else if" faster than "switch() case"?

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