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C++ Data Types


As you saw in the previous task, float's precision (7 decimal digits) is not always enough.
But C++ has a solution: double.
With a precision of 15 decimal digits, it is much more accurate than float.
The syntax of using double is the same as always:


By default, cout prints floating-point numbers with a precision of 6 significant digits.
That way, you won't see a difference between float and double.
To set a larger precision, you can use cout << setprecision(15); (this will set the precision to 15 significant digits).
However, you must include the iomanip library using #include<iomanip> in your program.



How is better precision achieved in double?
It just takes up more memory.
A float type takes up 4 bytes, and a double takes up 8 bytes of memory.

There also is a long double type.
Its size ranges from 8 bytes (just like a double) to 16 bytes.
You can check the size of the long double on your system by using the following code:

Additionally, you should add L to a value you are assigning (otherwise, the value will be assigned with the precision of double). Look at the example:

Here is a little summary:

Data TypeRangePrecision
float±1.2e-38 to ±3.4e+387 decimal digits
double±2.2e-308 to ±1.8e+30815 decimal digits
long doubledepends on a system but hugefrom 15 to 33 depending on a system

In the previous chapter, we converted a distance in kilometers to miles.
Let's see how precise those calculations were.

Here is an example of using double in the task from the previous chapter:




You need to calculate (1/3)² using different data types.
For that, assign the value of 1/3 to the float, double, and long double typed variables.
Then print those numbers multiplied by themselves, for example:


  1. Initialize a float variable with the value 1/3.;
  2. Initialize a double variable with the value 1/3.;
  3. Initialize a long double variable with the value 1/3.L.
    Note: long double takes up 16 bytes of memory on our system;
  4. Set the precision of output to 25 decimals with setprecision(25);
  5. Print all those values multiplied by themselves.


If you got zeros in the output, make sure you assigned the values exactly like shown above (1/3., 1/3.L).
We will discuss the reasons for this behavior in the Arithmetic Operations chapter.

Everything was clear?

Section 1. Chapter 8
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