This is my first GUI program in linux!

hello.glade

<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.18.3 -->
<interface>
  <requires lib="gtk+" version="3.12"/>
  <object class="GtkGrid" id="grid">
    <property name="visible">True</property>
    <property name="can_focus">False</property>
    <child>
      <object class="GtkButton" id="sayhello">
        <property name="label" translatable="yes">Say hello!</property>
        <property name="visible">True</property>
        <property name="can_focus">True</property>
        <property name="receives_default">True</property>
      </object>
      <packing>
        <property name="left_attach">1</property>
        <property name="top_attach">0</property>
      </packing>
    </child>
    <child>
      <object class="GtkEntry" id="output">
        <property name="visible">True</property>
        <property name="can_focus">True</property>
        <property name="editable">False</property>
      </object>
      <packing>
        <property name="left_attach">0</property>
        <property name="top_attach">1</property>
        <property name="width">2</property>
      </packing>
    </child>
    <child>
      <object class="GtkLabel" id="hh">
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="margin_left">24</property>
        <property name="margin_right">24</property>
        <property name="margin_top">12</property>
        <property name="margin_bottom">12</property>
        <property name="label" translatable="yes">Hi! this is my first GUI program in linux!</property>
      </object>
      <packing>
        <property name="left_attach">0</property>
        <property name="top_attach">2</property>
        <property name="width">2</property>
      </packing>
    </child>
    <child>
      <object class="GtkEntry" id="name">
        <property name="visible">True</property>
        <property name="can_focus">True</property>
        <property name="text" translatable="yes">Wtm</property>
        <property name="input_hints">GTK_INPUT_HINT_SPELLCHECK | GTK_INPUT_HINT_WORD_COMPLETION | GTK_INPUT_HINT_NONE</property>
      </object>
      <packing>
        <property name="left_attach">0</property>
        <property name="top_attach">0</property>
      </packing>
    </child>
  </object>
  <object class="GtkTextBuffer" id="textbuffer1"/>
</interface>

main.cc

#include <gtk/gtk.h>
#include <string>

using namespace std;

GtkWidget *box, *tep;

void say (GtkWidget* app, gpointer user_data)
{
    string sr = string(gtk_entry_get_text(GTK_ENTRY(box)));
    if(sr.size() == 0){
        sr = string("Hello! Input your name below then click the button.");
    }else{
        sr += string(", hello!");
    }
    gtk_entry_set_text(GTK_ENTRY(tep), (const gchar*)sr.c_str());
};

void activate (GtkApplication* app, gpointer user_data)
{
    GtkWidget *window;
    window = gtk_application_window_new(app);
    GtkBuilder * gtkb = gtk_builder_new_from_file("hello.glade");
    gtk_container_add(GTK_CONTAINER(window), GTK_WIDGET(gtk_builder_get_object(gtkb, "grid")));
    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER_ALWAYS);
    gtk_window_set_resizable(GTK_WINDOW(window), false);
    gtk_widget_show_all(window);

    box = GTK_WIDGET(gtk_builder_get_object(gtkb, "name"));
    tep = GTK_WIDGET(gtk_builder_get_object(gtkb, "output"));

    GObject *sayhello = gtk_builder_get_object(gtkb, "sayhello");
    g_signal_connect(sayhello, "clicked", G_CALLBACK(say), NULL);
};

int main (int argc, char **argv)
{
    GtkApplication *app;
    int status;

    app = gtk_application_new("org.websint.mao.hellogtk", G_APPLICATION_FLAGS_NONE);
    g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
    status = g_application_run(G_APPLICATION(app), argc, argv);
    g_object_unref(app);

    return status;
};

Makefile

everything:
	rm -f a.out
	g++ main.cc `pkg-config --cflags --libs gtk+-3.0`
	./a.out