switch Versus if-else Ladder : C programing Loop Control Structure

There are some things that you simply cannot do with a switch. These are:

(a)  A float expression cannot be tested using a switch
(b)  Cases can never have variable expressions (for example it is wrong to say case a +3 : )
(c)  Multiple cases cannot use same expressions. Thus the following switch is illegal

switch  ( a )

{
     case 3 :
  ...
     case 1 + 2 :
  ...

}

(a), (b) and (c) above may lead you to believe that these are obvious disadvantages with a switch, especially since there weren’t any such limitations with if-else. Then why use a switch at all? For speed—switch works faster than an equivalent if-else ladder. How come? This is because the compiler generates a jump table for a switch during compilation. As a result, during execution it simply refers the jump table to decide which case should be executed, rather than actually checking which case is satisfied. As against this, if-elses are slower because they are evaluated at execution time. A switch with 10 cases would work faster than an equivalent if-else ladder. Also, a switch with 2 cases would work slower than if-else  ladder. Why? If the 10th  case is satisfied then jump table would be referred and statements for the 10th case would be executed. As againstthis, in an if-else ladder 10 conditions would be evaluated at execution time, which makes it slow. 

Note that a lookup in the jump table is faster than evaluation of a condition, especially if the condition is complex.

If on the other hand the conditions in the if-else were simple and less in number then if-else would work out faster than the lookup mechanism of a switch. Hence a switch with two cases would work slower than an equivalent if-else. Thus, you as a programmer should take a decision which of the two should be used when.