C Tutorial Floating point types
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Floating point Types

float

Single precision floating point number

typical size: 32 bits

double

Double precision floating point number

typical size: 64 bits

 

long double Possibly even bigger floating point number (somewhat obscure)

Constants in the source code such as 3.14 default to type double unless the are suffixed with an 'f' (float) or 'l' (long double). Single precision equates to about 6 digits of

precision and double is about 15 digits of precision. Most C programs use double for their computations. The main reason to use float is to save memory if many numbers need to be stored. The main thing to remember about floating point numbers is that they are inexact. For example, what is the value of the following double expression?

 

(1.0/3.0 + 1.0/3.0 + 1.0/3.0)    // is this equal to 1.0 exactly?

 The sum may or may not be 1.0 exactly, and it may vary from one type of machine to another. For this reason, you should never compare floating numbers to eachother for equality (==) -- use inequality (<) comparisons instead. Realize that a correct C program run on different computers may produce slightly different outputs in the rightmost digits

of its floating point computations.


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