# C Math log10() Function

### Example

Return the base 10 logarithm of different numbers:

``````printf("%f", log10(120.0));
printf("%f", log10(10.0));
printf("%f", log10(3.1623));
printf("%f", log10(1.0));
printf("%f", log10(0.0));
printf("%f", log10(-1.0));
``````
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## Definition and Usage

The `log10()` function returns the base 10 logarithm of a number.

The `log10()` function is defined in the `<math.h>` header file.

Tip: The base 10 logarithm indicates approximately how many digits the integer part of a number has. See how to use it to count digits in the example below.

## Syntax

One of the following:

``log10(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 base 10 logarithm of a number.

## More Examples

### Example

Count the digits in a number:

``````double x = 1260.0;
int digits = floor( log10( x ) ) + 1;
printf("The number %f has %d digits.", x, digits);
``````

Try it Yourself »

## Related Pages

C Functions Tutorial

C Math Functions Tutorial

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