C Float

Summary: in this tutorial, you will learn about various C float types, including float, double, and long double.

Introduction to C float types #

Floating-point numbers are numbers that have a decimal point. For example, 3.14 is a floating-point number. C has two floating-point types:

• float: single-precision floating-point numbers
• double: double-precision floating-point numbers.

The following example uses the float and double keyword to define floating-point number variables:

#include <stdio.h>

int main( )
{
  float x = 0.1,
        y = 0.1,
        z = 0.1;

  float total = x + y + z;

  printf("The sum is %.20f\n", total);

  return 0;
}
Code language: C++ (cpp)

Output:

The sum is 0.30000001192092896000Code language: C++ (cpp)

How it works.

• First, define three floating-point numbers x, y, and z.
• Second, add three numbers up and display the result.

The sum of 0.1, 0.1, and 0.1 is not 0.3 but 0.30000001192092896000. This is due to the precision of the floating-point numbers.

What is precision? #

If you consider the fraction 5/3, this number can be represented in decimal as 1.666666666... with infinite 6.

Since computers use a fixed number of bits, they cannot store an infinite number. Instead, computers store these numbers with precision.

The precision is expressed as a number of significant digits. In other words, precision is defined as how many digits a number can represent without data loss.

For example, the float type with 4 bytes = 4 x 8 bits = 32 bits, is for numbers with single precision. It means that a float gives 1 sign bit, 8 bits of exponent, and 23 bits of significand.

The double type is for a number with the double-precision that gives 1 sign bit, 11 bits of exponent, and 52 bits of significand. (8 bytes x 8 bits = 64 bits = 1 bits + 52 bits + 11 bits).

Short and long qualifiers #

Like integers, you can apply the short and long qualifiers to control the size of the floating-point type. The following table shows the floating-point types in C.

It is important to note that this is only the minimal requirement for storage size defined by C.

Float ranges and precision #

To find the value ranges of the floating-point number, you can use the float.h header file. This header file defines macros such as FLT_MIN , FLT_MAX and FLT_DIG that store the float value ranges and precision of the float types.

The float.h also defines macros for double and long double with the prefixes DBL_ and LDBL_.

The following program illustrates your system’s storage size and precision of floating-point numbers.

#include <stdio.h>
#include <float.h>

int main( )
{
  printf("Storage size: %d bytes\n"
         "Minimum float value: %E\n"
         "Maximum float value: %E\n"
         "Precision: %d decimal digits\n",
         sizeof(float),
         FLT_MIN,
         FLT_MAX,
         FLT_DIG);

  puts("\nExample of float precision:\n");

  double d = 12345.6;
  float  f = (float)d;

  printf("The floating-point number d 18.10f\n", d);

  printf("Stored in a variable f of type float as the value %18.10f\n", f);

  return 0;
}Code language: C++ (cpp)

Summary #

• Floating-point numbers are numbers that have a decimal point.
• Use the float to declare the float variables.