Which is faster if-else or Switch case ?

• Oct 6, 2018

• #2

xwb

Programmer

Jul 11, 2002

6,828

GB

Depends on what you are doing - sometimes, it can be solved by simple arithmetic, which is faster than both. What exactly are you trying to do?

For example, if a number is 5, make it 2, if it is 2, make it 5. It could be coded as

Code:

' if statement - assuming it will only ever be 2 or 5
if x = 5 then
    x = 2
else
    x = 5
end if

' arithmetic - assuming it will only ever be 2 or 5
x = 7 - x

 

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• Oct 17, 2018

• #3

jbenson001

Programmer

Jan 7, 2004

8,172

US

Technically, a Switch / Case statement is faster because in an IF Statment, each IF / ElseIF is evaluated. In a Switch/Case, once the condition is met, the Switch/Case is exited.
Personally, I find Switch/Case to look cleaner and more readable as well. If it is just a small check as in xwb's example, then I would just use a standard IF or to shorten it I would use an InLine IF. The syntax differs between VB and C#

 

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• Oct 18, 2018

• #4

xwb

Programmer

Jul 11, 2002

6,828

GB

It really depends on the internal implementation of the switch statement.

If the cases are sequential, very often, the implementation is the equivalent of a computed goto. For example

Code:

    switch (x)
    {
    case 8: ...; break;
    case 5: ...; break;
    case 7: ...; break;
    case 6: ...; break;
    }

The compiler would arrange them as 5, 6, 7,8, subtract 5 from x and use a computed goto.

If the cases are not sequential, they could be sorted into a lookup table followed by a computed goto. Alternatively, it could be implemented as an if-elseif-else statement. If it is the latter then there is no difference between the switch and the if-elseif-else other than possibly elegance of the code.

 

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• Oct 19, 2018

• #5

jbenson001

Programmer

Jan 7, 2004

8,172

US

An IF statement will always evaluate each condition. A switch will fall through once the condition is met. True, depending on the conditions, they could be equal in performance, but the switch will win out in most cases.

 

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