How to set float to variable with 7 digits after the decimal point in arduino?

Question

Example:

float x = 3154681.124 / 100000; //x = 31.54;

I want x to be:

x = 31.5468112;

Answer 1

The float type has slightly over 7 digits of precision. See https://en.wikipedia.org/wiki/Floating_point.

I want x to be:

   x = 31.5468112;

Bad luck. That's 9 digits of precision. You can get around 7 digits by converting it appropriately, eg. as Majenko said:

  float x = 3154681.124 / 100000; //x = 31.54;
  Serial.println(x, 7);

However that printed:

31.5468101

It got 7 digits right, as advertised.

---

You can use the BigNumber Library that I wrote. Available from GitHub.

Using that, you can get all the precision you want, within reason:

#include "BigNumber.h"

void setup ()
  {
  Serial.begin (115200);
  Serial.println ();

  BigNumber::begin (7);  // 7 digits after the decimal place

  BigNumber x ("3154681.124");
  BigNumber y = x / BigNumber ("100000");
  
  Serial.println(y);
  }  // end of setup

void loop ()
  {
  }  // end of loop

Output:

31.5468112

Answer 2

float x = 3154681.124 / 100000; //x = 31.54;

x is now 31.5468112 (or close to).

Serial.println(x);

Output: 31.54

Why? Because Serial.println defaults to 2 decimal places for floats.

Syntax

Serial.println(val)

Serial.println(val, format)

Parameters

val: the value to print - any data type

format: specifies the number base (for integral data types) or number of decimal places (for floating point types)

So the solution: specift 7 decimal places when you print:

Serial.println(x, 7);