Clean up onboard_temperature example slightly, and let i tbuild when there is no default LED

Author: kilograham

adc/onboard_temperature/onboard_temperature.c

@@ -20,22 +20,24 @@ float read_onboard_temperature(const char unit) {
     /* 12-bit conversion, assume max value == ADC_VREF == 3.3 V */
     const float conversionFactor = 3.3f / (1 << 12);
 
-    float adc = adc_read() * conversionFactor;
-    float tempC = 27.0 - (adc - 0.706) / 0.001721;
+    float adc = (float)adc_read() * conversionFactor;
+    float tempC = 27.0f - (adc - 0.706f) / 0.001721f;
 
     if (unit == 'C') {
         return tempC;
     } else if (unit == 'F') {
         return tempC * 9 / 5 + 32;
     }
 
-    return -1.0;
+    return -1.0f;
 }
 
 int main() {
     stdio_init_all();
+#ifdef PICO_DEFAULT_LED_PIN
     gpio_init(PICO_DEFAULT_LED_PIN);
     gpio_set_dir(PICO_DEFAULT_LED_PIN, GPIO_OUT);
+#endif
 
     /* Initialize hardware AD converter, enable onboard temperature sensor and
      *   select its channel (do this once for efficiency, but beware that this
@@ -48,10 +50,12 @@ int main() {
         float temperature = read_onboard_temperature(TEMPERATURE_UNITS);
         printf("Onboard temperature = %.02f %c\n", temperature, TEMPERATURE_UNITS);
 
+#ifdef PICO_DEFAULT_LED_PIN
         gpio_put(PICO_DEFAULT_LED_PIN, 1);
         sleep_ms(10);
 
         gpio_put(PICO_DEFAULT_LED_PIN, 0);
+#endif
         sleep_ms(990);
     }