Add an example of undefined behaviour

.gitignore

@@ -27,3 +27,4 @@ mtrace-test
 mtrace-test.trace
 mtrace-test.txt
 av-variance
+undefined-behaviour

Makefile

@@ -2,7 +2,7 @@ CC=clang
 
 CFLAGS=-std=c99 -Wextra -pedantic -g -O0
 
-TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs ncurses-pong bit-fuckery bit-fuckery2 checkcheck multibrot bloom wo-lernen lua-foo binsearch test-inline-assembly uiowa-threads-example mtrace-test av-variance
+TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs ncurses-pong bit-fuckery bit-fuckery2 checkcheck multibrot bloom wo-lernen lua-foo binsearch test-inline-assembly uiowa-threads-example mtrace-test av-variance undefined-behaviour
 EXTRAS=mandelbrot.bmp multibrot.png test-inline-assembly.s tags mtrace-test.trace mtrace-test.txt
 
 .PHONY: all

undefined-behaviour.c

@@ -0,0 +1,16 @@
+#include <stdio.h>
+
+int main(void) {
+  int a = 5;
+  int b = a + 7;
+  int c = a - b + 7;
+
+  // c is zero now!
+  printf("c = %i\n", c);
+
+  // Depending on e.g. the optimization level, this either throws a
+  // floating point exception or does other things like returning 10.
+  if (3/c > 4)
+    return 5;
+  return 10;
+}