Xác định một yếu tố của một mảng hoàn toàn đủ điều kiện là thành viên của một cấu trúc dữ liệu cung cấp truy cập gián tiếp cho các thành viên trong một cấu trúc dữ liệu có địa chỉ được lưu trữ trong một con trỏ xác định các ưu tiên hoạt động (cũng có thể xem Phần 2,6) | Introduction to functions 69 fprintí stdout Co-ordinates x y of third point m. fscanf stdin lf lf triangle_2_ptr- x 2 triangle_2_ptr- y 2 return f Function calculate_area void calculate_area struct triangle triangle_ptr double a distance between points 1 and 2 7 b distance between points 2 and 3 7 c distance between points 3 and 1 7 s half perimeter of triangle 7 a sqrt triangle_ptr- x 1 - triangle_ptr- x O triangle_ptr- x 1J - triangle_ptr- x O triangle_ptr- y 1 - triangle_ptr- y O triangle_ptr- y 1 - triangle_ptr- y O b sqrt triangle_ptr- x 2 - triangle_ptr- x 1J triangle_ptr- x 2 - triangle_ptr- x 1 triangle_ptr- y 2 - triangle_ptr- y 1 triangle_ptr- y 2 - triangle_ptr- y 1 c sqrt triangle_ptr- x O - triangle_ptr- x 2 triangle_ptr- x O - triangle_ptr- x 2 triangle_ptr- y O - triangle_ptr- y 2 triangle_ptr- y O - triangle_ptr- y 2 s a b c triangle_ptr- area sqrt s s-a s-b s-c return Function write_area 7 void write_area struct triangle triangle_3 fprintí stdout Calculated area is lf m2 n return 70 c programming for scientists and engineers Looking at main a variable triangle_1 and a pointer triangle _l_ptr are both declared to be of data type struct triangle. Following this there is a function prototype statement for each function that main will use. These statements specify that main will pass a pointer of data type struct triangle to read_points and calculate_area. The function prototype for wiite_area specifies that main will pass a variable of type struct triangle by value. All of the function prototype statements specify that no data will be returned from any function via their return statements. The first executable statement in main copies the address of triangle_1 to triangle_1 _ptr. This is followed by statements that call each function in the required sequence. When read_points is called main passes the value of triangle_1 _ptr to it. This passes triangle_1 by reference to read_points. Note at this stage that no data values have been
