if...else if...else Statement

1. 流程圖
   
   
2. 語法

   if(boolean_expression 1) {
      /* Executes when the boolean expression 1 is true */
   }
   else if( boolean_expression 2) {
      /* Executes when the boolean expression 2 is true */
   }
   else if( boolean_expression 3) {
      /* Executes when the boolean expression 3 is true */
   }
   else {
      /* executes when the none of the above condition is true */
   }
   

3. 範例

   [dywang@deyu zzz]$ vim if4.c 
   [dywang@deyu zzz]$ cat if4.c 
   #include <stdio.h>
   
   int main() {
   	int a;
   
   	printf("Enter an integer: ");
   	scanf("%d", &a);
   
   	if ( a>10 ) {
   		printf("%d > 10\n", a);
   	}	
   	else if ( a<10) {
   		printf("%d < 10\n", a);
   	}	
   	else {
   		printf("a = 10\n");
   	}
   }
   

4. 編譯成功

   [dywang@deyu zzz]$ gcc -o if4 if4.c
   

5. 執行結果一

   [dywang@deyu zzz]$ ./if4
   Enter an integer: 20
   20 > 10
   

6. 執行結果二

   [dywang@deyu zzz]$ ./if4
   Enter an integer: 8
   8 < 10
   

7. 執行結果三

   [dywang@deyu zzz]$ ./if4
   Enter an integer: 10
   a = 10