Additional DigitalIn example

Revision:
0:10c4d3aa026e
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Thu Jan 19 14:21:24 2017 -0600
@@ -0,0 +1,17 @@
+#include "mbed.h"
+ 
+DigitalIn a(D0);
+DigitalIn b(D1);
+DigitalOut z_not(LED1);
+DigitalOut z_and(LED2);
+DigitalOut z_or(LED3);
+DigitalOut z_xor(LED4);
+ 
+int main() {
+    while(1) {
+        z_not = !a;
+        z_and = a && b;
+        z_or = a || b;
+        z_xor = a ^ b;
+    }
+}