Method to take temperature reading

This is the first step in separating the various things happening in the
main loop. Like the original, this method reads up to three times
looking for a non-zero value and returns immediately if one is read.

Unlike the original, this one uses errno to indicate no successful
reads.

temper.c

@@ -4,6 +4,7 @@
  */
 
 #include <stdio.h>
+#include <errno.h>
 #include <time.h>
 #include "pcsensor.h"
 
@@ -12,6 +13,28 @@
 static float scale = 1.0287;
 static float offset = -0.85;
 
+float read_temp() {
+  int i;
+  float tempc = 0.0000;
+
+  for (i = 0; i < 4; i++) {
+    usb_dev_handle* lvr_winusb = pcsensor_open();
+    if (!lvr_winusb) {
+      sleep(3);
+      continue;
+    }
+    tempc = pcsensor_get_temperature(lvr_winusb);
+    pcsensor_close(lvr_winusb);
+
+  /* Read can fail silently with a 0.0 return; repeat until we get a not zero
+   * value or until we have read a zero value 3 times (just in case the
+   * temperature really is zero */
+    if (tempc < -0.0001 || tempc > 0.0001) { return tempc; }
+  }
+  errno = ENOENT;
+  return tempc;
+}
+
 int main(){
   int passes = 0;
   float tempc = 0.0000;