Is "Else If" Faster Than "Switch() Case"

Is else if faster than switch() case ?

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.

Which is Faster and better, Switch Case or if else if?

Your first example is simply wrong. You need elseif instead of just else.

If you use if..elseif... or switch is mainly a matter of preference. The performance is the same.

However, if all your conditions are of the type x == value with x being the same in every condition, switch usually makes sense. I'd also only use switch if there are more than e.g. two conditions.

A case where switch actually gives you a performance advantage is if the variable part is a function call:

switch(some_func()) {
    case 1: ... break;
    case 2: ... break;
}

Then some_func() is only called once while with

if(some_func() == 1) {}
elseif(some_func() == 2) {}

it would be called twice - including possible side-effects of the function call happening twice. However, you could always use $res = some_func(); and then use $res in your if conditions - so you can avoid this problem alltogether.

A case where you cannot use switch at all is when you have more complex conditions - switch only works for x == y with y being a constant value.

Case vs If Else If: Which is more efficient?

It seems that the compiler is better in optimizing a switch-statement than an if-statement.

The compiler doesn't know if the order of evaluating the if-statements is important to you, and can't perform any optimizations there. You could be calling methods in the if-statements, influencing variables. With the switch-statement it knows that all clauses can be evaluated at the same time and can put them in whatever order is most efficient.

Here's a small comparison:

http://www.blackwasp.co.uk/SpeedTestIfElseSwitch.aspx

Is there any significant difference between using if/else and switch-case in C#?

SWITCH statement only produces same assembly as IFs in debug or compatibility mode. In release, it will be compiled into jump table (through MSIL 'switch' statement)- which is O(1).

C# (unlike many other languages) also allows to switch on string constants - and this works a bit differently. It's obviously not practical to build jump tables for strings of arbitrary lengths, so most often such switch will be compiled into stack of IFs.

But if number of conditions is big enough to cover overheads, C# compiler will create a HashTable object, populate it with string constants and make a lookup on that table followed by jump. Hashtable lookup is not strictly O(1) and has noticeable constant costs, but if number of case labels is large, it will be significantly faster than comparing to each string constant in IFs.

To sum it up, if number of conditions is more than 5 or so, prefer SWITCH over IF, otherwise use whatever looks better.

Javascript switch vs. if...else if...else

Answering in generalities:

1. Yes, usually.
2. See More Info Here
3. Yes, because each has a different JS processing engine, however, in running a test on the site below, the switch always out performed the if, elseif on a large number of iterations.

Test site

Why switch is faster than if

Because there are special bytecodes that allow efficient switch statement evaluation when there are a lot of cases.

If implemented with IF-statements you would have a check, a jump to the next clause, a check, a jump to the next clause and so on. With switch the JVM loads the value to compare and iterates through the value table to find a match, which is faster in most cases.

If vs. Switch Speed

The compiler can build jump tables where applicable. For example, when you use the reflector to look at the code produced, you will see that for huge switches on strings, the compiler will actually generate code that uses a hash table to dispatch these. The hash table uses the strings as keys and delegates to the case codes as values.

This has asymptotic better runtime than lots of chained if tests and is actually faster even for relatively few strings.

Is there any performance gain from using a switch statement over a bunch of if()else if() in javascript?

In general, switch is faster than if - else if statements.

However, kind of best practice is to use if - else if if you got max 3 conditionals. If you're going beyond that, you should use switch statements.

The problem with if else is that it possibly needs to check multiple times before it finally reaches the code to execute. Therefore you also need to optimize the order for your conditional statements.

if( foo ) {
}
else if( bar ) {
}
else if( baz ) {
}

That code would not make much sense from a performance prospective if you expect baz to be true and foo/bar to be false most of the times.

Which is better a switch statement or if-else if-else statement?

The compiler can create a jump table for certain types of switch statements which is more efficient than just evaluating each element like a nested set of if statements. This is dependent on the type of switch and the language you are working in, but many C compilers just this sort of thing in their code generation.

So the short is that a switch can be more efficient but it depends on your particular usage.

C# if else vs if or vs switch case

In some cases, an equivalent switch statement is slower than an if-statement or chain of if-statements. Using frequency heuristics, you can optimize a fast path with an if-statement in many programs.

See this Link you will find two different comparisons

http://www.dotnetperls.com/if-switch-performance

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