Question

int i = 10;

switch( i )
{
    case 1:
        // do sth1
        break;

    case 2:
        // do sth2
        break;

    case 3:
        // do sth3
        break;

    default:
        // do sth default
        break;
}

Question 1> When the switch statement executes, do we jump directly to the right case statement or do we search from top to bottom?

Answer: Directly jump to the right case statement.

Question 2> Should we use a break statement after the default statement?

Answer: Depends. If the default statement is the last case statement, then using break is NOT necessary.

Did I get the answers right in the above questions?

Answer 1

Question 1: Depends on the compiler. C++ standard does not require that a jump table be set up.

In many cases, especially with small number of sparse cases, GCC, MSVC and other compilers will do clause-by-clause check (as if it were an if statement). To give an example, suppose your cases were 1, 15, and 1000000. It would not be efficient code-wise to do a direct jump.

gcc has the option -fno-jump-tables to force it to build the equivalent if-else list.

Question 2: The break statement is not required for the last clause. It should be omitted if execution should flow down.