To create a desktop application in C, you can make use of frameworks and libraries that provide GUI (Graphical User Interface) functionality. One popular framework for developing desktop applications in C is GTK+ (GIMP Toolkit). GTK+ is a cross-platform toolkit that allows you to create GUI applications that can run on different operating systems such as Windows, macOS, and Linux.

Here's a step-by-step guide to creating a simple desktop application in C using GTK+:

Install the necessary tools:

Install a C compiler such as GCC (GNU Compiler Collection) for your operating system.

Install the GTK+ development libraries. The installation process may vary depending on your operating system.

Set up your development environment:

Create a new directory for your project.
Open a text editor or an Integrated Development Environment (IDE) to write your C code.
Write the C code:

Start by including the necessary GTK+ header files in your code:

#include <gtk/gtk.h>

Write the main function and initialize the GTK+ library:

int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);
    // Rest of your code goes here
    return 0;
}

Create a callback function that will be triggered when the application's window is closed:

static void on_window_closed(GtkWidget *widget, gpointer data) {
    gtk_main_quit();
}

Create the application window and connect the callback function to the "destroy" signal:

GtkWidget *window;

window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(window, "destroy", G_CALLBACK(on_window_closed), NULL);

Add additional GUI elements to your window, such as buttons, labels, or text fields, using GTK+ functions.

Display the window:

gtk_widget_show_all(window);

Start the GTK+ main loop:

gtk_main();

Compile and build the application:

Open a terminal or command prompt and navigate to your project directory.

Use the C compiler to compile your code, linking against the GTK+ libraries:

gcc -o your_application_name your_code.c `pkg-config --cflags --libs gtk+-3.0`

Run the application:

Execute the compiled binary file from the terminal or command prompt:

./your_application_name

This is a basic example to get you started with creating a desktop application in C using GTK+. You can explore the GTK+ documentation and tutorials for more advanced features and functionality. Additionally, other frameworks like Qt and wxWidgets also provide options for creating desktop applications in C, so you may consider exploring those as well.