The **`log10()` function** in D uses the base 10 to calculate the logarithm of a number. The figure below shows the mathematical representation of the `log10()` function.

> **Note**: We need to import `std.math` in our code, in order to use the `log10()` function. We can import it like this: <br>`import std.math`

# Syntax

Let's look at the syntax for the `log10()` function.

```d
// number should be float, double or real.
log10(number)
```

# Parameter
This function requires the #key# number: This number must be greater than 0. #key# for which the logarithm is to be calculated.

# Return value

`log10()` uses the base 10 to return the logarithm of a given number.

> **Note**:
>- If the parameter value is `positive infinity`, then the `log()` returns `positive infinity`.
>- If the parameter value is `NaN` or `negative infinity`, then the `log()` function returns `NaN`.
>- If the parameter value is `-NaN`, then the `log()` function returns `-NaN`.
>- If the parameter value is <= `0`, then the `log()` function returns `negative infinity`.

## Code example
The code written below shows us how to use the `log10()` function in D:

import core.stdc.stdio;
import std.stdio;
//header required for function
import std.math;

int main()
{
    //integer
    writeln ("The value of log10(10) : ",log10(10));

    //positive double value
    writeln ("The value of log10(2.56) : ",log10(2.56));

    //e
    writeln ("The value of log10(E) : ",log10(E));


    //exceptional outputs
    writeln ("The value of log10(-0.0) : ",log10(-0.0));
    writeln ("The value of log10(0.0) : ",log10(0.0));
    writeln ("The value of log10(real.infinity) : ",log10(real.infinity));
    writeln ("The value of log10(-real.infinity) : ",log10(-real.infinity));
    writeln ("The value of log10(real.nan) : ",log10(real.nan));
    writeln ("The value of log10(-real.nan) : ",log10(-real.nan));
    return 0;
}

## Code explanation
- **Line 4**: We add the header `std.math`, which is required for the `log10()` function.

-  **Line 9**: We calculate the log base 10 of the integer value, using the `log10()` function.

-  **Line 12**: We calculate the log base 10 of the positive double value, using the `log10()` function.

-  **Line 15**: We calculate the log base 10 of `e`, using the `log10()` function.

-  **Lines 18–25**: We calculate the log base 10 of `exceptional numbers`, using the `log10()` function.

What is the log10() function in D?

The log10() function in D computes the base-10 logarithm, requiring std.math import and input > 0.