Simple programs

Using ClearWin+, simple programs can be compiled unchanged. As soon as standard output is generated which would have gone to the screen, or the program attempts to read from the keyboard, a ClearWin window is set up by the ClearWin+ system. Successive lines of output are written to this window (entitled Output), which scrolls when necessary. The window acts like a terminal, so keyboard input is echoed in the window. The window can be scrolled, moved, or resized by the user. The system retains the information output to the window so that WM_PAINT messages can be handled without any special programmer action. As an example, here is a complete application program to calculate square roots:

       DO WHILE(.TRUE.)
         READ *,d
         PRINT *,SQRT(d)

Notice that this program does not require an explicit exit path. Each time it pauses for input, the system will be prepared to accept a window close request (Alt-F4). When your program exits, its window will remain open until closed by the user in order to ensure that the user has time to read the output.

Because ClearWin+ must store away every line that you send to a window - to cater for possible repaint requests or user scroll operations - it is important to limit the amount of output to manageable proportions. Store is consumed from the heap and is reclaimed when the ClearWin window is closed or cleared. It is recommended that the routine set_all_max_lines@ (or set_max_lines@) be used to limit the amount of store that is consumed.

In a similar way, DOS applications that contain calls to the Silverfrost graphics library can also be compiled unchanged. In this case ClearWin+ will automatically create a simple format window for the drawing.



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