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 0.30000001192092896000
Code 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 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, it cannot store an infinite number. Instead, computers store these numbers with precisions.

The precision is expressed as a number of significant digits. In other words, precision is defined as how many digits that 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 qualifier 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 the storage size and precision of floating-point numbers in your system.

#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