C Math log() Function
Example
Return the natural logarithm of different numbers:
const double E = 2.718281828;
printf("%f", log(6.0));
printf("%f", log(E));
printf("%f", log(2.0));
printf("%f", log(1.0));
printf("%f", log(0.0));
printf("%f", log(-1.0));
Definition and Usage
The log() function returns the natural logarithm of a number.
The log() function is defined in the <math.h> header file.
The natural logarithm is the logarithm with base e. The value of e is approximately 2.718282. Some implementations of the <math.h> library include a constant M_E but it is not guaranteed to be available.
Syntax
One of the following:
log(double number);Parameter Values
| Parameter | Description |
|---|---|
| number |
Required. Specifies the value to calculate the logarithm for. If the value is negative, it returns NaN (Not a Number). If the value is 0, it returns -infinity. |
Technical Details
| Returns: | A double value representing the natural logarithm of a number. |
|---|
