add a small union example

.gitignore

@@ -34,3 +34,4 @@ hello-openmp
 mandelbrot-openmp
 positional-format-strings
 uiowa-threads-my-example
+unions

Makefile

@@ -11,7 +11,7 @@ TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs \
 				uiowa-threads-example uiowa-threads-my-example \
 				mtrace-test av-variance undefined-behaviour \
 				multibrot-openmp hello-openmp mandelbrot-openmp \
-				positional-format-strings
+				positional-format-strings unions
 EXTRAS=mandelbrot.bmp multibrot.png test-inline-assembly.s \
 				mtrace-test.trace mtrace-test.txt multibrot-openmp.png
 VERYEXTRAS=cppcheck.txt macros.txt tags

unions.c

@@ -0,0 +1,14 @@
+#include <stdio.h>
+
+union u_tag {
+  int ival;
+  float fval;
+  char *sval;
+} u;
+
+int main() {
+  u.ival = 12;
+  printf("%f\n", u.fval);
+  u.fval = 0.01;
+  printf("%d\n", u.ival);
+}