Number of digits setting for serial printing the sensor output value I am getting fan motor rpm as 3200. But if I get the data as 50, I should get the value like 0050. How can I do this? 

I can do it like checking the value for single digit(0-9), double digit (10-99), and triple digit (100-999) and four digit(1000-9999). I need to fix digit size and send it through serial. Is there any other way for this?
You can use the C function sprintf: 

char text[5];
sprintf(text, "%04d", number);
Serial.println(text);


The leading 0 in 04d will add zero's for the length (4) is met, so 1 will become 0001, 10 will become 0010, 100 will become 0100 and 1000 will stay 1000.