# Real64 Data Type

Holds signed 64-bit (8-byte) IEEE floating-point values in the range −1.79769313486231570E+308 to −4.94065645841246544E−324 for negative values and 4.94065645841246544E−324 to 1.79769313486231570E+308 for positive values.

## Instructions

- Precision
- Know that floating-point data types cannot represent many values accurately. Operations such as comparisons can cause results that you think are incorrect. See Troubleshooting Data Types for more information.
- Space efficiency
- You can use
`Real64`

in conditions where the greater precision of`Real128`

is not necessary. Some conditions can let the ViviFire runtime reduce the memory that your program uses. - Default value
- When you declare a variable of type
`Real64`

and do not initialize it, its default value is zero (0.0). - Type changes
`Real64`

widens to`Real`

or`Real128`

without risk of overflow.- Trailing zeros
- The floating-point data types cannot internally represent trailing 0 characters after the decimal point. Thus numbers such as 1.4200 and 1.42 are the same value. If you must show trailing zeros, then you must use a formatter procedure.
- Type characters
`Real64`

has no type characters.

## Shared methods and properties

`Real64.Default As Real64`

- Returns the default value,
`0.0`

. `Real64.Epsilon As Real64`

- Returns the smallest difference between two values.
`Real64.IsInf(num As Real64) As Boolean`

- Returns true if
`num`

is infinity (positive or negative). Mathematical overflow is one cause of this result. `Real64.IsNaN(num As Real64) As Boolean`

- Returns true if
`num`

is not a number (Nan). “Zero divided by zero” and “square root of a negative” are two causes of this result. `Real64.IsNegInf(num As Real64) As Boolean`

- Returns true if
`num`

is negative infinity. `Real64.IsPosInf(num As Real64) As Boolean`

- Returns true if
`num`

is positive infinity. `Real64.Max As Real64`

- Returns the maximum positive value.
`Real64.Min As Real64`

- Returns the minimum negative value.
`Real64.Parse(str As String, Optional #fmt As Format) As Real64`

- Tries to parse a string that shows as a floating-point number.
- If
`#fmt`

is not given or is`#Null`

, then it uses the format of the local culture. Or you can be explicit with`Format.UserLocale`

. - If
`#fmt`

is`Format.RealLiteral`

, then it uses the format of a literal of type`Real64`

. `Real64.Size As Int`

- Returns the number of available bytes. This is always 8.

## Examples

```
Dim foo As Real64
```