switch statement

1. 流程圖
   
   
2. 語法：break 可有可無，有沒有 break 有何差別？

   switch(expression){
       case constant-expression  :
          statement(s);
          break; /* optional */
       case constant-expression  :
          statement(s);
          break; /* optional */
     
       /* you can have any number of case statements */
       default : /* Optional */
          statement(s);
   }
   

3. 範例

   [dywang@deyu zzz]$ vim sw1.c
   [dywang@deyu zzz]$ cat sw1.c
   #include <stdio.h>
   
   int main() {
   	char grade;
   	printf("Enter a char: ");
   	scanf("%c", &grade);
   
   	switch(grade) {
   	case 'A' :
   		printf("Excellent!\n" );
   		break;
   	case 'B' :
   	case 'C' :
   		printf("Well done\n" );
   		break;
   	case 'D' :
   		printf("You passed\n" );
   		break;
   	case 'F' :
   		printf("Better try again\n" );
   		break;
   	default :
   		printf("Invalid grade\n" );
   	}
   	printf("Your grade is  %c\n", grade );
   }
   

4. 編譯成功

   [dywang@deyu zzz]$ gcc -o sw1 sw1.c
   

5. 執行結果一

   [dywang@deyu zzz]$ ./sw1
   Enter a char: A
   Excellent!
   Your grade is  A
   

6. 執行結果一：輸入 A, C, D, F 都依判斷結果輸出。

   [dywang@deyu zzz]$ ./sw1
   Enter a char: C
   Well done
   Your grade is  C
   [dywang@deyu zzz]$ ./sw1
   Enter a char: D
   You passed
   Your grade is  D
   [dywang@deyu zzz]$ ./sw1
   Enter a char: F
   Better try again
   Your grade is  F
   

7. 執行結果二：輸入 B 時，沒有任何的執行敘述，而且沒有 break，所以不會跳出 case 判斷式，網續往下執行輸出 "well done"。

   [dywang@deyu zzz]$ ./sw1
   Enter a char: B
   Well done
   Your grade is  B
   

8. 執行結果三：輸入 E 及數字 43，都屬於最後的其他選項，輸出 "Invalid grade"。

   [dywang@deyu zzz]$ ./sw1
   Enter a char: E
   Invalid grade
   Your grade is  E
   [dywang@deyu zzz]$ ./sw1
   Enter a char: 43
   Invalid grade
   Your grade is  4