The simplest Windows program in C

Any software is designed with some functionality in mind. This functionality could include tasks such as reading external inputs, processing them in the way the engineer expects them to be processed, or accomplishing a specific function or task. All of these actions require interaction with the underlying operating system (OS). A program, in order to interact with the underlying OS, must call system functions. It might be nearly impossible to design a meaningful program that does not use any system calls.

In addition to that, in Windows, the programmer, when compiling a C program, needs to specify a subsystem (you can read more about it at https://docs.microsoft.com/en-us/cpp/build/reference/subsystem-specify-subsystem); windows and console are probably the two of the most common ones.

Let’s look at a simple example of a C program for Windows:

#include <Windows.h>
Int main(void) {
MessageBoxA(0, "hi there.", "info", 0);
return 0;
}

Presented here is the most simplified C program for Windows. Its purpose is to call the USER32!MessageBox() function at the entry point of the main() function to pop up a window with the info title and the hi there content.