函式參數

1. call by value
   

   /* function definition to swap the values */
   void swap(int x, int y)
   {
      int temp;
   
      temp = x; /* save the value of x */
      x = y;    /* put y into x */
      y = temp; /* put temp into y */
     
      return;
   }
   

   #include <stdio.h>
    
   /* function declaration */
   void swap(int x, int y);
    
   int main ()
   {
      /* local variable definition */
      int a = 100;
      int b = 200;
    
      printf("Before swap, value of a : %d\n", a );
      printf("Before swap, value of b : %d\n", b );
    
      /* calling a function to swap the values */
      swap(a, b);
    
      printf("After swap, value of a : %d\n", a );
      printf("After swap, value of b : %d\n", b );
    
      return 0;
   }
   

2. call by reference
   

   /* function definition to swap the values */
   void swap(int *x, int *y)
   {
      int temp;
      temp = *x;    /* save the value at address x */
      *x = *y;      /* put y into x */
      *y = temp;    /* put temp into y */
     
      return;
   }
   

   #include <stdio.h>
    
   /* function declaration */
   void swap(int *x, int *y);
    
   int main ()
   {
      /* local variable definition */
      int a = 100;
      int b = 200;
    
      printf("Before swap, value of a : %d\n", a );
      printf("Before swap, value of b : %d\n", b );
    
      /* calling a function to swap the values.
       * &a indicates pointer to a ie. address of variable a and 
       * &b indicates pointer to b ie. address of variable b.
      */
      swap(&a, &b);
    
      printf("After swap, value of a : %d\n", a );
      printf("After swap, value of b : %d\n", b );
    
      return 0;
   }