user58974: 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?

user31105: 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.

user16780: Three if statements look a bit simplistic, but are much better in code size than sprintf, if that's the only usage for sprintf.
 if (number < 1000) Serial.write('0');
 if (number < 100) Serial.write('0');
 if (number < 10) Serial.write('0');
 Serial.println(number);

Saves about 1.5kB Flash, compiled with Arduino 1.8.9 for an Uno 

58974: <p>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? </p>

<p>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?</p>


 31105: <p>You can use the C function <code>sprintf</code>: </p>

<pre><code>char text[5];
sprintf(text, "%04d", number);
Serial.println(text);
</code></pre>

<p>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.</p>
 16780: <p>Three if statements look a bit simplistic, but are much better in code size than <code>sprintf</code>, if that's the only usage for sprintf.</p>

<pre><code> if (number &lt; 1000) Serial.write('0');
 if (number &lt; 100) Serial.write('0');
 if (number &lt; 10) Serial.write('0');
 Serial.println(number);
</code></pre>

<p>Saves about 1.5kB Flash, compiled with Arduino 1.8.9 for an Uno </p>
