diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1e7500a..d0f12d9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,6 +16,7 @@ set(SOURCES
 	src/bar/init.c
 	src/bar/update.c
 	src/bar/draw.c
+	src/bar/change.c
 )
 
 set(ASSETS
diff --git a/include/bar.h b/include/bar.h
index ba58488..bbb25dc 100644
--- a/include/bar.h
+++ b/include/bar.h
@@ -13,8 +13,14 @@ struct Bar {
 	float fill;
 };
 
+#define BAR_TOTAL 4
 enum BarID { BAR_CASH, BAR_HUMAN, BAR_SMILE, BAR_SUN };
 
 struct Bar bar_init(enum BarID bar_id);
 void bar_update(struct Bar *bar);
 void bar_draw(struct Bar bar);
+/* Increase/decrease bar fill level.
+ * Return 1 when bar is fully filled.
+ * Return -1 when bar is fully emptied.
+ * Return 0 otherwise. */
+int bar_change(struct Bar *bar, float modifier);
diff --git a/src/bar/change.c b/src/bar/change.c
new file mode 100644
index 0000000..3f3ef19
--- /dev/null
+++ b/src/bar/change.c
@@ -0,0 +1,16 @@
+#include "bar.h"
+
+int
+bar_change(struct Bar *bar, float modifier)
+{
+	bar->fill += modifier;
+	if (bar->fill >= 1.0) {
+		bar->fill = 1.0;
+		return 1;
+	}
+	if (bar->fill <= 0.0) {
+		bar->fill = 0.0;
+		return -1;
+	}
+	return 0;
+}
diff --git a/src/bar/draw.c b/src/bar/draw.c
index 03d1706..ae3ec07 100644
--- a/src/bar/draw.c
+++ b/src/bar/draw.c
@@ -8,8 +8,8 @@ bar_draw(struct Bar bar)
 	const int y = bar.y + bar.height - height;
 
 	/* borders */
-	drect_border(bar.x - 1, bar.y - 1, bar.x + BAR_WIDTH + 1, bar.y + bar.height + 1,
-	             C_WHITE, 2, C_BLACK);
+	drect_border(bar.x - 1, bar.y - 1, bar.x + BAR_WIDTH + 1,
+	             bar.y + bar.height + 1, C_WHITE, 2, C_BLACK);
 	/* fill */
 	drect(bar.x, y, bar.x + BAR_WIDTH, y + height, C_RGB(0, 32, 32));
 }
diff --git a/src/main.c b/src/main.c
index 8d52cc4..8c80f02 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2,7 +2,7 @@
 #include <gint/display.h>
 #include <gint/keyboard.h>
 
-static struct Bar bars[4];
+static struct Bar bars[BAR_TOTAL];
 
 static void main_draw(void);
 
@@ -12,9 +12,12 @@ main(void)
 	int i;
 
 	/* init */
-	for (i = 0; i < 4; i += 1)
+	for (i = 0; i < BAR_TOTAL; i += 1)
 		bars[i] = bar_init(i);
 
+	bar_change(&bars[BAR_CASH], 0.2);
+	bar_change(&bars[BAR_SMILE], 0.4);
+
 	main_draw();
 	getkey();
 
@@ -33,7 +36,7 @@ main_draw(void)
 	dimage(0, 0, &bimg_background);
 
 	/* draw bars */
-	for (i = 0; i < 4; i += 1)
+	for (i = 0; i < BAR_TOTAL; i += 1)
 		bar_draw(bars[i]);
 
 	dupdate();