call by value

1. call by value：函式呼叫時傳入參數值，呼叫時複製一份給函式，不會影響目前的變數值。
2. 範例：輸入兩個數字，將其對換，呼叫時傳入變數的值。

   [dywang@dyw219 zzz]$ cat function2.c
   #include <stdio.h>
   
   void swap(int x, int y) {
   	int temp;
   
   	temp = x;
   	x = y;
   	y = temp;
   	return;
   }
    
   main() {
   	int a, b;
   
   	printf("Enter TWO integers: ");
   	scanf("%d %d", &a, &b);
   
   	printf("Before swap, a = %d, b = %d\n", a, b);
   	swap(a, b);
   	printf("After swap, a = %d, b = %d\n", a, b);
   }
   

3. 編譯成功

   [dywang@dyw219 zzz]$ gcc -o function2 function2.c
   

4. 執行結果：不論對換前後，原變數 a b 的數值皆不變。

   [dywang@dyw219 zzz]$ ./function2
   Enter TWO integers: 10 20
   Before swap, a = 10, b = 20
   After swap, a = 10, b = 20