Call by value: In call by value method, the called function creates a new set of variables and copies the values of arguments into them. Example: Program showing Call by value method

void swap(int x, int y)
{ 
  int temp;
  temp = x;
  x = y;
  y = temp;
  printf("Swapped values are a = %d and b = %d", x, y);
}

void main()
{
  int a = 7, b = 4;
  swap(a, b);
  printf("Original values are a = %d and b = %d", a, b);
  printf("The values after swap are a = %d and b = %d", a, b);
}

Output: Original Values are a = 7 and b = 4 Swapped values are a = 4 and b = 7

The values after swap are a = 7 and b = 4 This happens because when function swap() is invoked, the values of a and b gets copied on to x and y. The function actually swaps x and y while the original variables a and b remains intact.

Call by reference: In call by reference method, instead of passing a value to the function being called a reference/pointer to the original variable is passed. Example: Program showing Call by reference method

void swap(int *x, int *y)
{
  int temp;
  temp = *x;
  *x = *y;
  *y = temp;
  printf("Swapped values are a = %d and b = %d", *x, *y);
}
void main()
{
  int a = 7, b = 4;
  swap(&a, &b);
  printf("Original values are a = %d and b = %d",a,b);
  printf("The values after swap are a = %d and b = %d",a,b);
}

Output: Original Values are a = 7 and b = 4 Swapped values are a = 4 and b = 7

The values after swap are a = 4 and b = 7 This happens because when function swap() is invoked, it creates a reference for the first incoming integer a in x and the second incoming integer b in y.

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