Is the default option required in the switch statement?

The default option is not required in the switch statement. The switch statement will first look for the case value that meets the conditions as the program entry after execution. If all cases are not satisfied, it will look for the default entry. If not found, it will exit the entire statement; default is just a backup entry, and it does not matter whether it is present or not.

The operating environment of this tutorial: windows7 system, c99 version, Dell G3 computer.

Switch is a reserved word in some computer languages, and its function is to make judgments and selections in most cases; it is often used together with case, break, and default.

The switch statement can be used to perform different actions based on different conditions.

The switch statement is a conditional selection statement. First, the case value that meets the condition will be found as the program entry after execution; if all cases are not satisfied, the default entry will be found. If not found, the entire switch will be exited. statement; so default is just a backup entry, it doesn't matter whether it is present or not.

But for error checking or logic checking, the default branch should still be added to the switch statement.

For example, the following switch statement is completely legal:

switch (char_code)
{
      case tyt:
      case 'y': printf ( " You answered YES ! \n" )
           break
      case 'N':
      case 'n': printf ("You answered NO!\n");
           break
}

But what happens if an unknown character is passed to this switch statement? At this time, the program will have no output . Therefore, it is best to add a default branch to handle this situation:

......
default: printf ("Unknown response : %d\n", char_code);
          break
......

In addition, the default branch can bring a lot of convenience to logic checking. For example, if you use a switch statement to process a fixed number of conditions, and it is believed that values ​​outside these conditions are logical errors, you can add a default branch to identify logical errors.

Please see the following:

void move_cursor (int direction)
{
     switch (direction)
     {
           case UP:     cursor_up()
                            break
           case DOWN:   cursor_down()
                            break
           case LEFT:   cursor_left ()
                            break
           case RIGHT:  cursor_ right ( )
                             break
           default:     printf ("Logic error on line number %ld!!! \n",
                                     __ LINE__ )
                             break
     }
}

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