Advantage of switch over if-else statement

Question

What\'s the best practice for using a switch statement vs using an if statement for 30 unsigned enumerations where about 10 have an ex

Answer 1

When it comes to compiling the program, I don't know if there is any difference. But as for the program itself and keeping the code as simple as possible, I personally think it depends on what you want to do. if else if else statements have their advantages, which I think are:

allow you to test a variable against specific ranges you can use functions (Standard Library or Personal) as conditionals.

(example:

`int a;
 cout<<"enter value:\n";
 cin>>a;

 if( a > 0 && a < 5)
   {
     cout<<"a is between 0, 5\n";

   }else if(a > 5 && a < 10)

     cout<<"a is between 5,10\n";

   }else{

       "a is not an integer, or is not in range 0,10\n";

However, If else if else statements can get complicated and messy (despite your best attempts) in a hurry. Switch statements tend to be clearer, cleaner, and easier to read; but can only be used to test against specific values (example:

`int a;
 cout<<"enter value:\n";
 cin>>a;

 switch(a)
 {
    case 0:
    case 1:
    case 2: 
    case 3:
    case 4:
    case 5:
        cout<<"a is between 0,5 and equals: "<<a<<"\n";
        break;
    //other case statements
    default:
        cout<<"a is not between the range or is not a good value\n"
        break;

I prefer if - else if - else statements, but it really is up to you. If you want to use functions as the conditions, or you want to test something against a range, array, or vector and/or you don't mind dealing with the complicated nesting, I would recommend using If else if else blocks. If you want to test against single values or you want a clean and easy to read block, I would recommend you use switch() case blocks.

Answer 2

I'm not sure about best-practise, but I'd use switch - and then trap intentional fall-through via 'default'

Answer 3

The Switch, if only for readability. Giant if statements are harder to maintain and harder to read in my opinion.

ERROR_01 : // intentional fall-through

or

(ERROR_01 == numError) ||

The later is more error prone and requires more typing and formatting than the first.

Answer 4

I would say use SWITCH. This way you only have to implement differing outcomes. Your ten identical cases can use the default. Should one change all you need to is explicitly implement the change, no need to edit the default. It's also far easier to add or remove cases from a SWITCH than to edit IF and ELSEIF.

switch(numerror){
    ERROR_20 : { fire_special_event(); } break;
    default : { null; } break;
}

Maybe even test your condition (in this case numerror) against a list of possibilities, an array perhaps so your SWITCH isn't even used unless there definately will be an outcome.

Answer 5

switch is definitely preferred. It's easier to look at a switch's list of cases & know for sure what it is doing than to read the long if condition.

The duplication in the if condition is hard on the eyes. Suppose one of the == was written !=; would you notice? Or if one instance of 'numError' was written 'nmuError', which just happened to compile?

I'd generally prefer to use polymorphism instead of the switch, but without more details of the context, it's hard to say.

As for performance, your best bet is to use a profiler to measure the performance of your application in conditions that are similar to what you expect in the wild. Otherwise, you're probably optimizing in the wrong place and in the wrong way.

Answer 6

Compiler will optimise it anyway - go for the switch as it's the most readable.