để họ cung cấp một định nghĩa thông thường có sẵn cho tất cả các chức năng trong chương trình. Điều này hỗ trợ các đặc điểm kỹ thuật của giao diện giữa gọi điện thoại và được gọi là chức năng thông qua các báo cáo mẫu thử nghiệm chức năng trong chính. | Files and formatting 99 Function write_area Used in program . f Writes value of area passed from calling 7 function by value to file named by filename Ỉ which is also passed by value. int write_area char filename double area FILE output output fopen filename w fprintf output Area of triangle lf n area fclose output return O Program defines two structures struct triangle and struct file_names. Remember that these statements define these structures to be new data types that can be used in declaration statements. Also remember that these structures are defined outside of any function so that they provide a common definition available to all functions within the program. This supports the specification of interfaces between calling and called functions via the function prototype statements in main. Each function prototype specifies that the relevant function will receive either the value of a member within one of the data structures or it will receive the address of a structure via an appropriate pointer The first executable statements in main store the addresses of io and example in the relevant pointers. The remaining statements then call each of the functions as required. In calling read-filenames main passes io by reference. This allows read_filenames to store the names of the input and output files supplied by the user in io. When main calls read_points it passes the name of the input file by value and example by reference. The read-points function then uses the file name to open the input file by creating a stream called input. Having done this read-points reads the coordinates of three points and uses its copy of example_ptr called triangle_ptr in read-points to store them in example. Before leaving read-points the input file is closed because it is no longer needed. Function main then calls calculate_area which has not needed to be modified from the program considered in Chapter 3. Finally main calls write_area passing both the name of the 100 c .
