Learn C++ - C++ Floating-Point Numbers

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C++ floating point types represent numbers with fractional parts.

They provide a much greater range in values.

Literal

C++ has two ways of writing floating-point numbers.

The first is to use the standard decimal-point notation:

12.34             // floating-point 
987654.12         // floating-point 
0.12345           // floating-point 
8.0               // still floating-point 

The second method called E notation, and it looks like this: 3.45E6.

This means that the value 3.45 is multiplied by 1,000,000.

E6 means 10 to the 6th power, which is 1 followed by 6 zeros.

Thus 3.45E6 means 3,450,000.

The 6 is called an exponent, and the 3.45 is termed the mantissa.

Here are more examples:

1.12e+8             // can use E or e, + is optional 
1.12E-4             // exponent can be negative 
7E5                 // same as 7.0E+05 
-12.12e13           // can have + or - sign in front 

Example

The following code examines types float and double.

#include <iostream> 
using namespace std; 
int main() /*from  w w w .jav  a  2s.  c o m*/
{ 
     cout.setf(ios_base::fixed, ios_base::floatfield); // fixed-point 
     float tub = 10.0 / 3.0;     // good to about 6 places 
     double mint = 10.0 / 3.0;   // good to about 15 places 
     const float million = 1.0e6; 

     cout << "tub = " << tub; 
     cout << ", a million tubs = " << million * tub; 
     cout << 10 * million * tub << endl; 

     cout << "mint = " << mint << " and a million mints = "; 
     cout << million * mint << endl; 
     return 0; 
} 

The code above generates the following result.

Floating-Point Constants

By default, floating-point constants such as 8.24 and 2.4E8 are type double.

If you create a constant to be type float, you use an f or F suffix.

For type long double, you use an l or L suffix.

Here are some samples:

1.234f         // a float constant 
2.45E20F       // a float constant 
2.345324E28    // a double constant 
2.2L           // a long double constant 

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