The Case Control Structure

Question 1

switch-case-default

Answer 1

Allows us to make decisions from many choices.

switch (int output Exp)
case (constant 1) : { statement(s); }
break;
case (constant 2) : { statement(s); }
break;
default : { statement(s); }
If no case satisfied then default is executed. Case satisfied when that int matches with constant of case.

Question 2

Use of break in switch-case-default

Answer 2

Its use is optional. If break is not used then the case which satisfies will get executed and all the subsequent cases and finally default.

Question 3

Some tips of switch:

Answer 3

1. Order of cases can be random.

2. u can use char value in case and switch. As said before, the use of ASCII values happens.

Question 4

Execute the same set of Statements for multiple cases:

Answer 4

switch (int output Exp)
   case (constant 1): 
   case (constant 2) : { statement(s); }
                     break;
   case (constant 3):
   case (constant 4) : { statement(s); }
                     break;
                  default : { statement(s); }

Cuz remember once a case satisfied everything is executed until break is encountered or switch block completes.

Question 5

Braces and case?

Answer 5

Well no need of braces for a block of case, cuz since satisfied it will run till break occurs or switch block is completed. But u can, y not, for neatness.

Question 6

What if there is a statement which does not belong to any case?

Answer 6

Then compiler won’t report an error but its never executed.

Question 7

What if no default case:

Answer 7

then program simply falls through entire switch and instruction after the closing brace of switch is executed if any.

Question 8

Advantage of if Over Switch:

Answer 8

The case cant be i <= 20, it has be something that gets evaluated to int or char value not even float.

Question 9

Advantage of switch over if:

Answer 9

Neat, easy life.

more so if multiple statements within each case.

Question 10

Case expressions:

Answer 10

constant exp allowed.
case a + b: invalid
case 3+7: valid.

Question 11

Continue and switch:

Answer 11

use of continue will not take the control to the beginning of switch.

Question 12

nested switch:

Answer 12

Allowed but not preferred.

Question 13

same expressions case?

Answer 13

It illegal.

Question 14

Why is switch used even though it has so many limitations:

execution of switch by compiler:

Answer 14

Compiler generates a jump table for switch during compilation. compiler simply looks at jump table to decide which case to execute rather than actually checking if each case is satisfied.

Lookup in a jump table is faster than evaluation of a condition (10)especially complex one.

but simple and less conditions (2) in if-else would work faster than corresponding switch.

Question 15

exit() function:

Answer 15

Standard lib function.

Terminates the execution of the program.

Question 16

About goto:

why use it or avoid it:

Answer 16

The writer says, avoid it. As we can never be sure how we got to a certain point and it can always be avoided with good programming skills. It makes debug tedious.

Its preferred when we want to take control out of loop which is contained in several loops.

Question 17

goto example:

Answer 17

main()
{
  for(i=0;i<=3;i++)
   {
       for(j=0;j<=3;j++)
        {
             for(k=0;k<=3;k++)
                {
                   if(i==3&amp;&amp;j==3&amp;k==3)
                     goto out;
                   else
                       print("%d%d%d",i,j,k);
                  }
          }
   }
  exit()
  out:
        printf("Woo all are equal");
}